Module 2 Compulsory Reading - Kandel, Schwartz, Jessell, third edition

Chapter 2, pg. 26-32, Receptor activation: in chemical synaptic transmission-pages 131-132.

Chapter 23, pg. 329-339: adequate stimulation, sensory threshold, duration, location, sensory receptors, rapidly and slowly adapting receptors, intensity and frequency and population, receptor potential, receptor specificity 

Chapter 24, pg. 341-352: Dorsal root ganglion neuron-sensory receptors 

Chapter 33, pg. 502-503: Vestibular hair cells, Pages 565-569: Muscle spindles and golgi tendon organs; page 575: 1a afferents and monosynaptic connections to motor neurons, Page 569: secondary endings, Page 568: muscle stretch receptors

 Chapter 37: muscle receptors and stretch reflexes

 Chapter 49, pg 770-771: Baroreceptors, carotid sinus and blood pressure control

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 TI: Ultrastructural basis for synaptic transmission between jaw-muscle spindle afferents and trigeminothalamic neurons in the rostral trigeminal sensory nuclei of the rat.AU: Luo-P; Wong-R; Dessem-DAD: Department of Physiology, University of Maryland Dental School, Baltimore 21201-1586, USA.SO: J-Comp-Neurol. 1995 Dec 4; 363(1): 109-28 -ISSN: 0021-9967

AB: Trigeminothalamic neurons were retrogradely labeled by injection of horseradish peroxidase into the ventroposteromedial nucleus of the thalamus in rats. Jaw-muscle spindle afferent axons were then physiologically identified and intracellularly stained with biotinamide. The ultrastructure of labeled spindle afferent boutons was then studied in the caudolateral supratrigeminal region (Vsup) and dorsomedial trigeminal principal sensory nucleus (Vpdm). A total of 418 stained spindle afferent boutons were identified in Vsup and Vpdm; approximately 75% of these synapsed with dendrites, 10% synapsed with somata, and 15% synapsed with axons. Most jaw-muscle spindle afferent boutons were postsynaptic to unlabeled P-type boutons. Reciprocal synapses between spindle afferent boutons and unlabeled boutons were occasionally observed. A few dendrites in Vsup and Vpdm received synapses from multiple spindle afferent boutons. Conversely, some large (from 3 x 6 to 4 x 8 microns) and giant (from > 4 x 8 to 5 x 10 microns) spindle afferent boutons simultaneously contacted two to five dendrites and/or somata. Jaw-muscle spindle afferent boutons also formed synapses with retrogradely labeled trigeminothalamic neurons in Vsup and Vpdm. Numerous unlabeled S-and F-type boutons converged onto the same trigeminothalamic dendrite or soma contacted by a spindle afferent bouton. A small number of synaptic triads consisting of an unlabeled P-type bouton, a spindle afferent bouton, and either a dendrite or soma were also encountered. These data indicate that sensory feedback from the masticatory muscles is subject to presynaptic inhibition and integration prior to reaching the thalamus. This pathway is likely to be important in the relay of proprioceptive and kinesthetic information from the muscles of mastication to the thalamus.

TI: Closed-loop control of ankle position using muscle afferent feedback with functional neuromuscular stimulation.AU: Yoshida-K; Horch-KAD: Department of Bioengineering, University of Utah, Salt Lake City 84112, USA.SO: IEEE-Trans-Biomed-Eng. 1996 Feb; 43(2): 167-76-ISSN: 0018-9294

AB: This paper describes a closed-loop functional neuromuscular stimulation system that uses afferent neural activity from muscle spindle fibers as feedback for controlling position of the ankle joint. Ankle extension against a load was effected by neural stimulation through a dual channel intrafascicular electrode of a fascicle of the tibial nerve that innervated the gastrocnemius muscle. Ankle joint angle was estimated from recordings of tibialis anterior and lateral gastrocnemius spindle fiber activity made with dual channel intrafascicular electrodes. Experiments were conducted in neurally intact anesthetized cats and in unanesthetized decerebrate cats to demonstrate the feasibility of this system. The system was able to reach and maintain a fixed target ankle position in the presence of a varying external moment ranging in magnitude between 7.3 and 22 N-cm opposing the action of the ankle extensor, as well as track a sinusoidal target ankle position up to a frequency of 1 Hz in the presence of a constant magnitude 22- or 37-N-cm external moment.

 TI: Peripheral target specification of synaptic connectivity of muscle spindle sensory neurons with spinal motoneurons.AU: Wenner-P; Frank-EAD: Neurobiology Department, University of Pittsburgh, School of Medicine, Pennsylvania 15261, USA.SO: J-Neurosci. 1995 Dec; 15(12): 8191-8-ISSN: 0270-6474

AB: The source of environmental cues determining the central connections of muscle sensory neurons was investigated by manipulating chick embryos so that sensory neurons supplied a duplicate set of dorsal thigh muscles. These neurons projected out ventral nerve pathways and along motor axons that normally project to ventral muscles but their ultimate target tissue was the duplicate set of dorsal muscles. The central connections of these sensory neurons to motoneurons supplying normal dorsal muscles were then determined with intracellular recordings in isolated spinal cord preparations. Sensory neurons supplying individual duplicate dorsal muscles made the same connections as those supplying the corresponding normal dorsal muscles; the pattern of these connections was different than that made by afferents supplying ventral muscles. Sensory neurons thus made synaptic connections appropriate for their target muscle rather than for their more proximal ventral environment. These findings suggest that the target muscle is the source of cues that determine the central connections of the sensory neurons projecting to it. Motoneurons forced to innervate novel muscle received many of the same sensory inputs they would normally receive, suggesting that motoneurons are less influenced by their target tissue than sensory neurons.

 TI: Prenatal development of somatosensory primary afferent connections in the sheep.AU: Rees-S; Nitsos-I; Rawson-JAD: Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Vic., Australia.SO: Reprod-Fertil-Dev. 1995; 7(3): 427-30ISSN: 1031-3613

AB: A summary is presented of recently published studies on the structural and functional development of cutaneous and muscle receptors and the connections of their afferent fibres in fetal sheep (n = 26) aged between 67 and 143 days gestation (term, 146 days). In these studies it was shown that primary afferent fibres projected to, and made synaptic connections with, dorsal horn neurons in lumbosacral spinal cord by 56-61 days gestation. Sensory innervation of the skin occurred later by about 75 days gestation and, at this age, stimulation of the skin first activated cutaneous afferent fibres and evoked a discharge in dorsal root ganglion and dorsal horn neurons. Muscle stretch first activated muscle spindles and evoked a discharge in dorsal root ganglion cells by about 75 days. Prior to this (by about 67 days) primary afferent fibres had begun to innervate motoneuron pools in the spinal cord, and motor nerves had begun to innervate muscle fibres. Both muscle spindle and cutaneous innervation were relatively simple at mid gestation indicating that the structure of sensory receptors need not be complex in order to generate a response. Neural pathways necessary for reflex activity involving muscle spindles are therefore present and functional by mid gestation as are cutaneous pathways projecting from the skin to the spinal cord.

 TI: The fusimotor system. Its role in fatigue.AU: Hagbarth-KE; Macefield-VG-AD: Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden.

AB: Several lines of evidence point to an important role of the fusimotor system in the "muscle-wisdom" phenomenon during peripheral fatigue of some human voluntary contractions: 1) muscle afferents provide a net amplification of skeletomotor output, with the only known afferent species capable of this being the muscle spindle; 2) muscle spindle firing rates decline during constant-force voluntary contractions, so fusimotor support to skeletomotor output decreases; 3) this waning support can be offset by application of high-frequency vibration to the fatiguing muscle, which excites spindle endings; and 4) the progressive decline in motor unit firing rates during maximal voluntary contractions is abolished by blocking muscle afferent inputs, and it is argued that, at least in the initial stages of a contraction, this must be due to a progressive withdrawal of spindle support.

 TI: Ia boutons to CCN neurones and motoneurones are enriched with glutamate-like immunoreactivity.AU: Ornung-G; Ragnarson-B; Grant-G; Ottersen-OP; Storm-Mathisen-J; Ulfhake-B-AD: Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.SO: Neuroreport. 1995 Oct 23; 6(15): 1975-80ISSN: 0959-4965

AB: The monosynaptic connection between muscle spindle Ia afferents and motoneurones is one of the most extensively studied reflex pathways in the central nervous system. Physiological evidence has pointed to glutamate as the fast transmitter in this synaptic connection. In this study of the spinal cord segment C2, we used dual labelling with cholera toxin subunit B-horseradish peroxidase (B-HRP) and postembedding immunohistochemistry to show that group Ia primary afferent boutons synapsing on retrogradely labelled central cervical nucleus (CCN) neurones and motoneurones are enriched in glutamate-like immunoreactivity (LI). All double-labelled Ia terminals studied could be classified as S-type (CCN neurones and motoneurones) or M-type (motoneurones) boutons.

 TI: Increased resting discharge of human spindle afferents following voluntary contractions.AU: Wilson-LR; Gandevia-SC; Burke-D-AD: Department of Clinical Neurophysiology, Prince Henry and Prince of Wales Hospitals, University of New South Wales, Sydney, Australia.SO: J-Physiol-Lond. 1995 Nov 1; 488 ( Pt 3): 833-40-ISSN: 0022-3751

AB: 1. The aim of this study was to assess the incidence of lasting alterations in discharge rate of muscle spindle afferents innervating human ankle and toe dorsiflexor muscles following isometric contractions. 2. The subjects performed controlled isometric ankle dorsiflexions maintained for approximately 5 s. During the contraction the discharge of all but one spindle afferent increased above the precontraction level. After complete relaxation, there was prolonged enhancement of the discharge rate of nineteen of fifty-five muscle spindle afferents and none of three Golgi tendon organ afferents. Ten of the nineteen spindle afferents had been silent prior to the contraction. For the population of fifty-five spindle afferents, the mean 'postcontraction' discharge rate was 65% higher than the mean precontraction discharge rate, with the mean rate increasing from 2.3 to 3.9 Hz (P < 0.001). The mean duration of the enhanced postcontraction discharge was 52 s (range, 8-240 s). 3. Stretch applied to the tendon of the receptor-bearing muscle in twelve of fourteen spindle afferents with an enhanced postcontraction discharge rate eliminated or reduced the enhanced discharge rate. 4. The high incidence of an enhanced spindle discharge after voluntary contraction (35% of spindle afferents) suggests that muscle 'history' should be taken into account when interpreting changes in spindle discharge rates. The enhanced discharge rates following contraction probably reflect a long-lasting effect of the contraction-associated increase in fusimotor drive on intrafusal stiffness, rather than the persistence of fusimotor drive following relaxation.MESH: Adult-; Forearm-physiology; Muscle,-Skeletal-innervation; Muscle,-Skeletal-physiology; Muscle,-Skeletal-ultrastructure; Neurotendinous-Spindles-physiology

 TI: Third-order reverse correlation analysis of muscle spindle primary afferent fiber responses to random muscle stretch.AU: Kroller-J-AD: Department of Physiology, Freie Universitat, Berlin, Germany.

AB: The response of primary muscle spindle afferent fibers to muscle stretch is nonlinear. Now spindle responses (trains of action potentials) to band-limited Gaussian white noise length perturbations of the gastrocnemius muscles (input signal) are described in cats. The input noise upper cutoff frequency was clearly above the frequency range of physiological length changes in cat hindleg muscles. The input-output relation was analyzed by means of peri-spike averages (PSAs), which could be shown to correspond to the kernels of Wiener's white noise approach to systems identification. The present approach (the reverse correlation analysis) was applied up to the third order. An experiment consisted of two recordings: one (the source recording) to determine PSAs and the other (the test recording) to provide an input signal for predicting responses. The predictions of different orders were compared with the actual neuronal response (the observation) of the test recording. Four different approximation procedures were developed to adapt prediction and observation and to determine weighting factors for the predictions of different orders. The approximations also yielded the value of the power density P of the input noise signal: at a variety of stimulus parameters, P from approximations had the same magnitude as P determined directly from the input signal amplitude spectrum. The prediction of a sequence of action potentials improved the higher the order of components. 37 of 42 action potentials of a test recording (the observation) could be confidently predicted from PSAs or kernels. Compared with the size of the linear first-order prediction curve, the relative sizes of the second and third-order prediction curves were: 1.0:0.47:0.26.MESH: Action-Potentials-physiology; Afferent-Pathways-physiology; Cats-; Cybernetics-; Electrophysiology-; Mathematics-; Models,-Biological; Muscle,-Skeletal-cytology; Predictive-Value-of-Tests

TI: The role of the gamma-system for improving information transmission in populations of Ia afferents.AU: Bergenheim-M; Johansson-H; Pedersen-JAD: Division of Work Physiology, National Institute of Occupational Health, Umea, Sweden.SO: Neurosci-Res. 1995 Sep; 23(2): 207-15-ISSN: 0168-0102

AB: Ensemble coding of simple mechanical stimuli (small sinusoidal stretches) was studied in populations of simultaneously recorded primary muscle spindle afferents (MSAs). The experiments were made on 39 primary MSAs in chloralose anaesthetised cats. For the analyses we used a combination of principal component analysis and algorithms for quantification of stimulus discrimination. Ensembles of primary MSAs discriminated better between different muscle stretches than individuals, and showed a successive increase in discriminative ability with increasing ensemble size. The ensemble effect disappeared after cutting the ventral roots, indicating an important role for the fusimotor system in ensemble coding. Simultaneously recorded ensembles of MSAs showed significantly better discriminative ability than pooled sequentially recorded MSAs. This difference was abolished by the cutting of the ventral roots. It is hypothesised that, since the muscle spindles are connected to each other via secondary MSAs (projecting to gamma-motoneurones to other spindles), the fusimotor-muscle spindle system may constitute a neural network, in which each 'neuron' (i.e., each individual muscle spindle) is influenced by the activity in the whole network. In populations of pooled sequentially recorded MSAs, the connections would not exist. Thus, the population would lose its neural network quality, and the encoding ability of the population would decrease. 

TI: Influences on the gamma-muscle spindle system from muscle afferents stimulated by increased intramuscular concentrations of bradykinin and 5-HT.AU: Djupsjobacka-M; Johansson-H; Bergenheim-M; Wenngren-BI-AD: Division of Work Physiology, National Institute of Occupational Health, Umea, Sweden.SO: Neurosci-Res. 1995 Jun; 22(3): 325-33-ISSN: 0168-0102

AB: There is evidence that static muscular contractions induce a release of bradykinin (BK) in the working muscle, and that increased concentration of BK and 5-HT in a muscle increases the discharge rate of a subpopulation of group III and group IV muscular afferents. It is also known that activity in group III and IV muscle afferents may activate gamma-motoneurones to both homonymous and heteronymous muscles. The aim of the present study was to investigate whether increased concentration of BK and 5-HT in one muscle may influence the activity in primary and secondary muscle spindle afferents (MSAs) from the chemically affected muscle and from surrounding muscles, via fusimotor reflexes. The experiments were made on six cats anaesthetised with alpha-chloralose. The triceps surae (GS) and the posterior biceps and semitendinosus (PBSt) muscles were subjected to sinusoidal stretches. Simultaneous recordings of 2-11 MSAs from these muscles were made and the mean rate of firing and the modulation for each MSA were determined. Responses of 47 MSAs (26 PBSt and 21 GS) were recorded. The responsiveness of the MSAs to injections of BK (9-100 mg/ml, 0.5-1.0 ml) and 5-HT (25-150 mg/ml, 0.5-1.0 ml) was 89% and 83%, respectively, for injections into the arterial supply of the ipsilateral GS muscle, and 84% and 40% respectively for injections to the contralateral GS muscle. Of 10 secondary MSAs, only one was unresponsive to BK injections, while several MSAs responded to both ipsilateral and contralateral BK injections.

TI: Effects of L-DOPA on fusimotor control of triceps surae muscle spindles in the cat.AU: Johansson-H; Sjolander-P; Sojka-P; Wenngren-BI-AD: Division of Work Physiology, National Institute of Occupational Health, Umea, Sweden.SO: Neurosci-Res. 1995 Jun; 22(3): 307-14-ISSN: 0168-0102

AB: The experiments were performed on lightly alpha-chloralose anaesthetised and spinalized cats. Alterations in fusimotor activity were assessed by recordings from single spindle afferents (90 primary and 12 secondary) from the triceps surae muscle, before and after i.v. administration of L-beta-3,4-dihydroxyphenylalanine (L-DOPA). The effects of L-DOPA on fusimotor reflexes from ipsi- and contralateral hind limb afferents were investigated by using extensions of the intact contralateral hind limb and tonic stretches of the ipsilateral posterior biceps and semitendinosus muscles as reflex stimuli. Prior to injection of L-DOPA, a low reflex responsiveness was found to both the ipsi- and the contralateral stimulation. After administration of L-DOPA, the reflex responsiveness as well as the resting activity of the muscle spindle afferents were increased as a result of enhanced activity in mainly dynamic fusimotor neurones. The results indicate that changes in fusimotor activity elicited after administration of L-DOPA are caused by release of transmission in interneuronal pathways mediating ipsi- and contralateral reflexes to mainly dynamic fusimotor neurones. The possible role of monoaminergic descending control of fusimotor neurones in the regulation of muscle tone, tremor and rigidity is discussed.MESH: Afferent-Pathways-drug-effects; Cats-; Injections,-Intravenous; Nialamide-pharmacology; Reflex-drug-effects 

TI: Ankle extensor group I afferents excite extensors throughout the hindlimb during fictive locomotion in the cat.AU: Guertin-P; Angel-MJ; Perreault-MC; McCrea-DA-AD: Department of Physiology, University of Manitoba, Winnipeg, Canada.SO: J-Physiol-Lond. 1995 Aug 15; 487 ( Pt 1): 197-209-ISSN: 0022-3751

AB: 1. The effects of stimulating hindlimb extensor nerves (100-200 ms trains, 100 Hz, < or = 2 times threshold) during the flexor and extensor phases of the locomotor step cycle were analysed in the decerebrate, paralysed cat during fictive locomotion evoked by stimulation of the mesencephalic locomotor region. 2. Stimulation during extension of either the medial gastrocnemius (MG), lateral gastrocnemius-soleus (LGS) or plantaris (Pl) nerves was equally effective in increasing the duration and amplitude of electroneurogram (ENG) activity recorded in ipsilateral ankle, knee and hip extensor nerves. Enhancement of extensor ENG activity could be evoked with near threshold stimulation intensity and appeared within 10-40 ms of the onset of ankle extensor nerve stimulation. Stimulation of anterior biceps during extension occasionally evoked a modest increase in the duration of activity of hip, knee and ankle extensors. Stimulation of quadriceps during extension enhanced the activity of proximal extensors and soleus, but inhibited other ankle extensors. 3. Selective activation of ankle extensor Ia spindle afferents by muscle stretch also enhanced ipsilateral extension. It is argued that both muscle spindle and tendon organ afferents can contribute to the increase in extensor nerve activity evoked by group I stimulation intensity during fictive locomotion. 4. During flexion, stimulation of either the MG, Pl or LGS nerves at group I strength terminated on-going activity in ipsilateral flexors and initiated a burst of activity in ipsilateral hip, knee and ankle extensors, i.e. reset the step cycle to extension. 5. Low strength stimulation of the mixed muscle and cutaneous nerve innervating the plantar aspect of the foot produced extension enhancement and resetting similar to that evoked by group I muscle afferent stimulation. Stimulation of the cutaneous nerve supplying the dorsal aspect of the foot during extension enhanced extensor activity, and during flexion, enhanced the activity of flexors. 6. The effects reported hre during fictive locomotion may also occur during overground locomotion with natural activation of group I muscle spindle and tendon organ afferents. Extensor spindle and tendon organ afferents may thus serve as an excitatory reflex system helping to shape the amplitude, duration and timing of ipsilateral extensor activity. Increased or unexpected activation of group I ankle extensor afferents or plantar foot afferents during locomotion could also compensate for increased loading of the limb.

 TI: Serial E-M and simulation study of presynaptic inhibition along a group Ia collateral in the spinal cord.AU: Walmsley-B; Graham-B; Nicol-MJ-AD: Neuroscience Group, Faculty of Medicine, University of Newcastle, Callaghan, New South Wales, Australia.SO: J-Neurophysiol. 1995 Aug; 74(2): 616-23-ISSN: 0022-3077

AB: 1. A muscle spindle primary afferent (group Ia) was physiologically identified and labeled intracellularly with the use of horseradish peroxidase (HRP) in the cat lumbar spinal cord. Serial-section electron microscopy (EM) was used to examine and reconstruct an entire axon collateral and its branches within Clarke's column. In the present study the existence and location of presynaptic contacts on Ia afferent boutons along these collateral branches were determined from examination of the serial-section electron-micrographs. 2. Of 36 Ia boutons examined in serial sections along the branches of the same collateral, 3 presynaptic contacts were found. Two of these contacts were made with Ia boutons in a complex nodal region consisting of two unmyelinated side branches exhibiting a total of six Ia boutons. The other presynaptic contact was made with a Ia bouton in a nodal region consisting of two Ia boutons connected by a thin unmyelinated bridge. 3. Computer simulations, based directly on the serial-section-reconstructions, were used to investigate the possible effects of these presynaptic contacts on membrane potential and on a propagating action potential along the Ia collateral. The effect of a presynaptic contact was modeled by a sustained gamma-aminobutyric acid-A (GABAA)-activated chloride conductance. 4. The simulation results indicated that the effect of a presynaptic contact on membrane potential and action-potential amplitude is likely to extend beyond the contacted bouton to other boutons occurring along the short unmyelinated branches arising from the same node.(ABSTRACT TRUNCATED AT 250 WORDS)

TI: Effects of afferent firing frequency on the amplitude of the monosynaptic EPSP elicited by trigeminal spindle afferents on trigeminal motoneurones.AU: Grimwood-P; Appenteng-K-AD: Department of Physiology, University of Leeds, UK.-SO: Brain-Res. 1995 Aug 21; 689(2): 299-303-ISSN: 0006-8993

AB: We have examined the effect of changes in afferent firing frequency on the monosynaptic EPSP elicited by trigeminal muscle spindle afferents in elevator motoneurones, using both paired pulse and repetitive activation of the masseter nerve. Both modes of stimulation resulted in significant facilitation of EPSP amplitude over intervals of 5-19 ms, but no significant change in EPSP amplitude at either longer or shorter intervals. The facilitation obtained stands in contrast to the predominant depression of EPSP amplitude reported in hindlimb motoneurones following stimulation at decreasing intervals. 

TI: Oscillations in the discharge frequency of cat primary muscle spindle afferents during the dynamic phase of a ramp-and-hold stretch. AU: Schafer-SS-AD: Department of Neurophysiology, Medical School of Hannover, FRG.-SO: Brain-Res. 1995 Jul 17; 686(1): 61-9-ISSN: 0006-8993

AB: Under a ramp-and-hold stretch the Ia afferent responds to the beginning of the ramp phase with an initial frequency peak, which is followed during the ongoing dynamic phase of stretching by further frequency peaks. In this investigation the behavior of the initial peak is compared with the behavior of the subsequent peaks under four experimental conditions: (i) increasing prestretch of the muscle, (ii) increasing stretch rate, (iii) change in the waiting time before a ramp stretch, (iv) variations in the degree of prestretch preceding a ramp stretch, which is then started from a medium degree of prestretch. Under three of these four experimental conditions the initial peak behaves qualitatively differently from the subsequent peaks. This result gives rise to the interpretation that the causes of the initial peak and the subsequent peaks are different. The initial peak is caused by a largely synchronous opening of acto-myosin bonds in the polar parts, whereas the subsequent peaks may be caused by intrinsic oscillatory properties of the receptor potential. 

TI: Differences in the brain stem terminations of large- and small-diameter vestibular primary afferents.-AU: Huwe-JA; Peterson-EH-AD: Department of Biological Sciences, College of Arts and Sciences, Ohio University, Athens 45701, USA.-SO: J-Neurophysiol. 1995 Sep; 74(3): 1362-6-ISSN: 0022-3077

AB: 1. We visualized the central axons of 32 vestibular afferents from the posterior canal by extracellular application of horseradish peroxidase, reconstructed them in three dimensions, and quantified their morphology. Here we compare the descending limbs of central axons that differ in parent axon diameter. 2. The brain stem distribution of descending limb terminals (collaterals and associated varicosities) varies systematically with parent axon diameter. Large-diameter afferents concentrate their terminals in rostral regions of the medial/descending nuclei. As axon diameter decreases, there is a significant shift of terminal concentration toward the caudal vestibular complex and adjacent brain stem. 3. Rostral and caudal regions of the medial/descending nuclei have different labyrinthine, cerebellar, intrinsic, commissural, and spinal connections; they are believed to play different roles in head movement control. Our data help clarify the functions of large- and small-diameter afferents by showing that they contribute differentially to rostral and caudal vestibular complex.

TI: Weight judgment. The discrimination capacity of a deafferented subject.AU: Fleury-M; Bard-C; Teasdale-N; Paillard-J; Cole-J; Lajoie-Y; Lamarre-Y-AD: Laboratoire de Performance Motrice Humaine, Universite Laval, Quebec, Canada.-SO: Brain. 1995 Oct; 118 ( Pt 5): 1149-56-ISSN: 0006-8950

AB: A weight discrimination study was undertaken to test (i) the capacity of controls and a deafferented subject (deprived of large sensory myelinated fibres from nose down), to discriminate weights with and without vision; (ii) the capacities of observers to discriminate weights while watching the deafferented and control subjects' lifting movements; (iii) the contribution of supplementary sources of sensory information (e.g. vestibular afferents) to the deafferented subject's discrimination capacity. With vision, G.L.'s liminal discrimination of weights was similar to that of the controls. In contrast, precluding vision impaired massively, but not completely, G.L.'s discrimination capacity, so emphasizing the importance of visual kinaesthetic cues in G.L. and incidently the importance of large myelinated sensory function in weight discrimination in controls. Kinematics recordings of G.L.'s lifting movements with vision revealed a significant correlation between weight and peak velocity of the lifting movement. This reflects a specific strategy used by G.L. to generate movements, allowing her to judge the weight of a lifted object visually. Peak velocity rather than amplitude of movement appears to be the main cue for G.L. since there was a lack of correlation between amplitude and weight lifted. For controls, none of the correlations (weight versus amplitude or weight versus velocity) was significant, whether vision was available or not. When watching G.L.'s lifting performance, external observers were able to use similar cues to establish their judgments, but they were far less accurate in doing so when watching control subjects. This suggests that controls were using a strategy different from G.L.'s.(ABSTRACT TRUNCATED AT 250 WORDS)

TI: The effect of continuous epidural infusion of ropivacaine (0.1%, 0.2% and 0.3%) on nerve conduction velocity and postural control in volunteers.-AU: Zaric-D; Nydahl-PA; Adel-SO; Enbom-H; Magnusson-M; Philipson-L; Axelsson-K-AD: Department of Anaesthesiology, Lund University of Hospital, Sweden.-SO: Acta-Anaesthesiol-Scand. 1996 Mar; 40(3): 342-9-ISSN: 0001-5172

AB: BACKGROUND: Continuous epidural infusions of local anaesthetics have become increasingly popular in postoperative pain treatment, especially as they permit early mobilisation. Ropivacaine is a promising new agent which induces more pronounced sensory than motor blockade. This study was focused on the influence of continuous epidural infusion of ropivacaine on impulse conduction in large nerves (by measurement of F and H latencies), and on the subjects' ability to maintain postural control during mobilisation. METHODS: Healthy male volunteers received 0.1%, 0.2% or 0.3% ropivacaine, and bupivacaine 0.25% was used as reference. A bolus epidural injection of 10 ml of the drug, at L2/3 level, was followed by continuous infusion at 10 ml/h for 21 h. Motor blockade was assessed by mechanical measurements of force during big toe flexion and by recording of F latency. Sensory blockade was monitored by pin-prick and Thermotest methods, and by H latency recording. The subjects' ability to perform a postural test was evaluated by posturography. RESULTS: The F and H latencies became prolonged/abolished dose-dependently. With ropivacaine, F latency recovered significantly later than motor function (P = 0.0002), and H latency recovered later than normal pin-prick perception (P = 0.0006). However, the duration of partial blockade of thermoperception was comparable to that of H latency prolongation. Posturographically, the subjects receiving 0.1% ropivacaine differed significantly from all others (P < 0.001) in that they were able to maintain postural control during the infusion. The recovery period after termination of infusion was significantly shorter with ropivacaine than with bupivacaine for all measured variables. CONCLUSION: Recovery of postural control with 0.2% and 0.3% ropivacaine is significantly faster than with bupivacaine 0.25%. H latency recording allows detection of epidural blockade intensity that does not prevent subjects from performing postural tests.

 TI: Pure stimulus-sensitive truncal myoclonus of propriospinal origin.AU: Schulze-Bonhage-A; Knott-H; Ferbert-A-AD: Neurologische Klinik, Stadtische Kliniken Kassel, Germany.SO: Mov-Disord. 1996 Jan; 11(1): 87-90-ISSN: 0885-3185

AB: The clinical and electrophysiological features of stimulus-sensitive truncal myoclonus are described in a 49-year-old woman. Touching the skin of the back and abdomen would evoke jerks in both ipsilateral and contralateral axial muscles; there was no spontaneous jerking. Multichannel EMG recordings showed bilateral short-latency muscle bursts at truncal recording sites both rostral and caudal to stimulus sites. The short latencies of muscle bursts in adjacent segments give evidence of a spinal origin of myoclonus; the pattern of recruitment and the velocity of spread suggest the involvement of propriospinal pathways. The presence of intrathecal IgG synthesis and of oligoclonal bands in the CSF point towards an inflammatory process which may underly the unusual type of myoclonus in this patient.

TI: Changing of an isolated neurone ultrastructure during a prolonged impact of mediator.-AU: Fedorenko-GM; Gusatinsky-VN; Kaminsky-II; Kondratyeva-LA; Korzak-VM-AD: A. B. Kogan Research Institute for Neurocybernetics, Rostov-on-Don, Russia.-SO: Neuroreport. 1995 Nov 27; 6(17): 2325-32-ISSN: 0959-4965

AB: We investigated the influence of prolonged excitation or combined excitation/inhibition on the ultrastructural changes in an isolated stretch receptor neurone from crayfish abdomen. Excitatory impulse activity was achieved by mechanical stimulation of a neurone for 10 or 120 min and inhibition of the activity was obtained by perfusion with gamma-aminobutyric acid (GABA, 2.5 x 10(-5) M) for the same periods. Changes in the ultrastructural components were observed following both excitatory and inhibitory stimulation for 120 min. Neuronal adaptation to excitatory or inhibitory stimuli after 120 min resulted in the appearance of an increased number of the giant mitochondria. Thus, the number of giant mitochondria may serve as an ultrastructural index of the degree of neuronal adaptation to external stimulation.

TI: [Neurocardiogenic (or vasovagal) syncope]-TO: La sincope neurocardiogena (o vasovagale).-AU: Cafagna-D; Ponte-E-AD: Prima Divisione di Medicina Generale, Ospedale di Cattinara, Trieste.-SO: Minerva-Med. 1996 May; 87(5): 207-15-ISSN: 0026-4806

AB: Syncope is a common clinical problem in a general population that is responsible for a significant number of emergency department visits (3%) and hospitalizations (1%) each year. The clinical spectrum of etiologies of syncope includes disorders classified as cardiovascular, noncardiovascular and unexplained. A majority of syncopal events are believed to be caused by vasovagally mediated episodes by hypotension and bradycardia. Although vasovagal syncope is essentially equivalent to simple fainting, the physiologic events that lends to this phenomena are complex. Although not completely understood, the most commonly held theory explaining vasovagal syncope involves a series of reflexive interactions between cardiac mechanoreceptors and the autonomic nervous system. Until the advent of head upright tilt table testing, diagnosis of vasovagal syncope has been an assumption, made when all other causes have been eliminated. Frequently an accurate history, a physical examination and a standard ECG are enough to formulate a correct diagnosis. Head-up tilt test must be considered in patients with an unknown diagnosis, before starting invasive investigation. Tilt table testing, either alone or with a graded-dose infusion of isoproterenol, allows reproduction of the syncopal event in susceptible individuals and monitoring of the patients physiologic responses during the episode. Direct observation and documentation of symptoms permit accurate diagnosis and yield information vital to treatment and symptom control. This article reviews our current understanding of the mechanisms involved in the development of neurally mediated syncope.

TI: 'Aortic baroreceptor' neurons in the nucleus tractus solitarius in rats: convergence of cardiovascular inputs as revealed by heartbeat-locked activity. AU: Nosaka-S; Murase-S; Murata-K; Inui-K-AD: Department of Physiology, Mie University School of Medicine, Japan.-SO: J-Auton-Nerv-Syst. 1995 Oct 5; 55(1-2): 69-80-ISSN: 0165-1838

AB: Rat aortic depressor nerve (ADN) contains only baroreceptor afferents. We identified 'aortic baroreceptor' neurons in the nucleus tractus solitarius (NTS) as those responding to electrical stimulation of the ADN and attempted to demonstrate convergence of cardiovascular mechanoreceptor inputs in these 'baroreceptor' neurons. In chloralose-urethane-anesthetized rats, ADN stimulation evoked either short or long latency responses (SLR, LLR) in 193 neurons of the NTS. 28 (SLR, 15; LLR, 13) demonstrated ongoing activities with cardiac rhythm despite the fact that the ADN had been cut peripherally. In 12 (SLR, 5; LLR, 7) of the 28 neurons, heartbeat-locked activity was abolished by carotid occlusion (CO), and augmented by methoxamine-induced blood pressure elevation, indicating that the heartbeat-locked activity originated from carotid sinus baroreceptors (CSB). In 11 neurons (SLR, 6; LLR, 5), the heartbeat-locked activity was not affected by CO but was abolished by topical application of lidocain on the ipsilateral cervical vagus, suggesting that the heartbeat-locked activity originated mostly from cardiac mechanoreceptors. The origin of the heartbeat-locked activity of the remaining 5 neurons could not be determined. The onsets, as well as peaks of the heartbeat-locked activity of vagal origin appeared significantly earlier than those of CSB origin. In conclusion, NTS neurons receive converging projection not only from the two major arterial baroreceptors but also from the arterial baroreceptors and cardiac mechanoreceptors, thereby integrating sensory information of vascular and cardiac origins.

 TI: Calcitonin gene-related peptide is involved in the spinal processing of mechanosensory input from the rat's knee joint and in the generation and maintenance of hyperexcitability of dorsal horn-neurons during development of acute inflammation.-AU: Neugebauer-V; Rumenapp-P; Schaible-HG-AD: Physiologisches Institut, Universitat Wurzburg, Germany.-SO: Neuroscience. 1996 Apr; 71(4): 1095-109-ISSN: 0306-4522

AB: In an electrophysiological study in anaesthetized rats, the involvement of calcitonin gene-related peptide in the spinal processing of mechanosensory information from the normal and inflamed knee joint was investigated. Calcitonin gene-related peptide(8-37), a specific antagonist at calcitonin gene-related peptide 1 receptors was administered ionophoretically close to nociceptive neurons with input from the knee joint before, during, and after development of acute inflammation in the knee induced by the intra-articular injections of kaolin and carrageenan. Calcitonin gene-related peptide (8-37) selectively antagonized the effects of ionophoretically applied calcitonin gene-related peptide but not those of ionophoretically applied substance P, neurokinin A, and (R,S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid. Before inflammation, calcitonin gene-related peptide (8-37) reduced the responses to noxious pressure applied to the knee in 22 of 23 neurons; in 14 of 22 neurons, the responses to innocuous pressure were also reduced. In eight neurons calcitonin gene-related peptide (8-37) was administered during induction and in three periods within the first 90 min of inflammation. In these neurons the developing inflammation evoked a significantly smaller increase of the responses to innocuous and noxious pressure applied to the injected knee than in 13 control neurons which were not treated by the antagonist during induction of inflammation. In 16 of 16 neurons, calcitonin gene-related peptide (8-37) reduced the responses to innocuous and noxious pressure once inflammation and hyperexcitability of the spinal cord neurons were established. These data show that calcitonin gene-related peptide is involved in the spinal processing of mechanosensory input from the normal joint. Furthermore, this peptide and its spinal receptors significantly contribute to the generation and expression of inflammation-evoked hyperexcitability of spinal cord neurons during the development of inflammation. Finally, calcitonin ene-related peptide is involved in the maintenance of inflammation-evoked hyperexcitability. By these effects calcitonin gene-related peptide receptors may significantly contribute to the neuronal basis of hyperalgesia and allodynia associated with inflammation.

TI: Number and morphology of mechanoreceptors in the myotendinous junction of paralysed human muscle.-AU: Jozsa-L; Kannus-P; Jarvinen-TA; Balint-J; Jarvinen-M-AD: Department of Morphology, National Institute of Traumatology, Budapest, Hungary.-SO: J-Pathol. 1996 Feb; 178(2): 195-200-ISSN: 0022-3417

AB: The mechanoreceptor system of the myotendinous junction (MTJ) of human palmaris longus muscle obtained at autopsy was studied histologically from six patients with flaccid paralysis (complete acute tetraplegia 4-6 weeks before the autopsy, due to a spinal cord injury), eight patients with spastic paralysis (chronic hemiplegia due to cerebral stroke) and ten neurologically normal controls. Four types of nerve endings, Ruffini and Pacini corpuscles, Golgi tendon organs, and free nerve endings, could be identified in the MTJs of the controls. In the MTJs of the patients with flaccid and spastic paralysis, the free nerve endings were not present and the mechanoreceptors that were found were few in number, degenerated, fibrotic, and atrophic. These mechanoreceptors had lost their connection with the muscle fibres and tendon bundles and were frequently located within pathological accumulations of fatty tissue in the myotendinous region. The number and distribution of mechanoreceptors in the MTJ were almost identical in patients with flaccid and spastic paralysis.

TI: A dynamic network simulation of the nematode tap withdrawal circuit: predictions concerning synaptic function using behavioral criteria.-AU: Wicks-SR; Roehrig-CJ; Rankin-CH-AD: Program in Neuroscience, University of British Columbia, Vancouver, Canada.-SO: J-Neurosci. 1996 Jun 15; 16(12): 4017-31-ISSN: 0270-6474

AB: The nematode tap withdrawal reflex demonstrates several forms of behavioral plasticity. Although the neural connectivity that supports this behavior is identified (Integration of mechanosensory stimuli in Caenorhabditis elegans, Wicks and Rankin, 1995, J Neurosci 15:2434-2444), the neurotransmitter phenotypes, and hence whether the synapses in the circuit are excitatory or inhibitory, remain uncharacterized. Here we use a novel strategy to predict the polarity configuration, i.e., the array of excitatory and inhibitory connections, of the nematode tap withdrawal circuit using an anatomically and physiologically justifiable dynamic network simulation of that circuit. The output of the modeled circuit was optimized to the behavior of animals, which possessed circuits altered by surgical ablation by exhaustively enumerating an array of synaptic signs that constituted the modeled circuit. All possible polarity configurations were then compared, and a statistical analysis was used to determine whether, for a given synaptic class, a particular polarity was associated with a good fit to behavioral data. The results from four related experiments were used to predict the polarities of seven of the nine cell classes of the tap withdrawal circuit. In addition, the model was used to assess possible roles for two novel mechanosensory integration neurons: DVA and PVD.

TI: Somatosensory evoked potentials following voluntary movement during upper arm compression.-AU: Nishihira-Y; Araki-H; Funase-K; Imanaka-K; Suzuki-J; Takemiya-T-AD: Division of Physiology, Institute of Health and Sport Sciences, University of Tsukuba, Ibaraki, Japan.-SO: Electromyogr-Clin-Neurophysiol. 1996 Jan-Feb; 36(1): 21-8-ISSN: 0301-150X

AB: We examined the modulation of somatosensory evoked potentials (SEPs) during upper arm compression and following voluntary movement during upper arm compression. Most SEPs were significantly decreased, although some SEPs showed a slight, non-significant diminution. SEPs are mediated not only by myelinated fibers but also by mixed nerves and afferents from cutaneous, joints, and deep tissues, these being dependent upon the dorsal column-medical lemniscal system. Therefore, most of the diminution in SEPs found here may have been due to afferent occlusion from muscle, cutaneous, joints, and deep tissues, since normal SEPs are selectively modulated, corresponding to motor or mental tasks, regardless of whether gating is centrifugal or centripetal. In addition, the present experiments showed that all the SEPs at FZ, C3' and CZ were significantly decreased following voluntary movement at a pressure 25%-30% higher than the subject's systolic blood pressure. Comparing SEPs during upper arm compression and those following voluntary movement during upper arm compression at these pressures, we found that the SEPs at C3' were significantly diminished following voluntary movement during upper arm compression, with other SEPs showing slight, non-significant attenuation. In conclusion, it is possible that the diminution in SEPs following voluntary movement could be responsible for sensory inputs, however, when sensory inputs are present, centrifugal modulation would also be responsible for this diminution.

TI: [Neurocardiogenic syncope: its pathogenesis, diagnosis and treatment]-TO: Sincope neurocardiogenica: patogenia, diagnostico e tratamento.-AU: Freitas-J; Puig-J; Pizarro-M; Costa-O; Carvalho-M; de-Freitas-AF-AD: Centro de Estudos da Funcao Autonomica, Hospital de Sao Joao, Porto, Portugal.-SO: Rev-Port-Cardiol. 1996 Feb; 15(2): 103-9, 99-AB: Neurocardiogenic syncope seems to be the most common cause of syncope. It is believed to be triggered by paradoxical autonomic reflexes, beginning in the ventricular mechanoreceptors of the heart, modulated by the brain stem and terminating in the autonomic efferent pathways (parasympathetic stimulation with bradycardia or asystole and sympathetic inhibition with severe hypotension). Tilt test has been used recently, as a safety and effective tool to identify subjects prone to syncope. Although the pathophysiology of this syndrome is not completely understood, pharmacological therapeutics seems very effective in resolving symptoms.

TI: New insights into the pathophysiology of carotid sinus syndrome.-AU: Tea-SH; Mansourati-J; L'Heveder-G; Mabin-D; Blanc-JJ-AD: Laboratoire de Neurophysiologie, Universite de Bretagne Occidentale, Brest, France.-SO: Circulation. 1996 Apr 1; 93(7): 1411-6-ISSN: 0009-7322

AB: BACKGROUND: The pathophysiology of carotid sinus syndrome remains poorly understood. Currently, two main hypotheses are provided: a lesion at the level of carotid sinus receptors or a central defect at the level of the nuclei of the autonomic nervous system. The objective of our study was to present arguments in favor of one of these two hypotheses. METHODS AND RESULTS: Test selection was guided by the following hypothesis: a degenerative central or local lesion could be associated with dysfunctions in the structures surrounding or comprising the baroreflex centers or their pathways. To test this hypothesis, brain stem auditory-evoked potentials; somatosensory-evoked potentials; blink reflexes; sympathetic skin responses; and styloglossus, sternocleidomastoid, and superior trapezius muscle electromyography were systematically performed from the right and left sides in 17 patients with carotid sinus syndrome and in 17 sex- and age-matched control subjects. Similar responses were found in the two groups for the "central" tests. Contrasting with this result, the electromyographic analysis of the sternocleidomastoid muscle differed significantly between the groups: 13 (76%) had pathological responses in the carotid sinus syndrome group compared with only 4 (23.5%) in the control group (P < .01). Furthermore, the abnormality was found on the right and left sides in 9 patients (53%) in the study group and in none of the control group (P < .005). CONCLUSIONS: This study strongly suggests that the neuromuscular structures surrounding the carotid mechanoreceptors are involved in the carotid sinus syndrome; however, the exact mechanism remains speculative.

TI: The sensory innervation of the shoulder joint of the mouse.-AU: Backenkohler-U; Halata-Z; Strasmann-TJ-AD: University of Hamburg, Department of Functional Anatomy, Germany.-SO: Anat-Anz. 1996 Apr; 178(2): 173-81-ISSN: 0003-2786

AB: The ultrastructure and location of sensory nerve endings in the shoulder-joint capsule, its tendinous reinforcements and in the periarticular connective and muscle tissue have been studied by means of light and electron microscopy in adult female white NMRI-F2 laboratory mice, aged 2.5-13 months. Most of the sensory nerve endings were detected in the fibrous layer of the joint capsule or in the inserting tendons. The identified lamellated corpuscles of the Pacini type are small and sometimes associated with Golgi tendon-organs. Large Vater-Pacini corpuscles were not detected. Ruffini corpuscles are found in small numbers only in the moderately dense connective tissue of the joint capsule. Golgi tendon organs were found mainly at the muscle-tendon junction of the muscles surrounding the joint. Muscle spindles have been identified mainly in periarticular muscles close to the muscle-tendon junctions. The number and distribution of the different types of mechanoreceptors investigated in the present study suggest that periarticular corpuscular sensory nerve endings play an important role in shoulder-joint control and mobility. The occurrence of small uniformly shaped lamellated corpuscles of the Pacini type in qualitatively different areas of surrounding tissue implies that they are susceptible to different kinds of mechanical stimuli. 

TI: Responses of mechanoreceptor neurons in the cat knee joint capsule before and after anterior cruciate ligament transection.-AU: Khalsa-PS; Grigg-P-AD: University of Massachusetts Medical School, Worcester, 01655, USA.-SO: J-Orthop-Res. 1996 Jan; 14(1): 114-22-ISSN: 0736-0266

AB: It is known that afferent neurons play a protective role in knees made unstable by transection of the anterior cruciate ligament. However, it is not known whether cutting the anterior cruciate ligament has an effect on the response of the sensory neurons that innervate the joint. In this study, the responsiveness (activation threshold and position sensitivity) of single, mechanically sensitive afferent neurons from the cat knee was evaluated by a series of extension, internal, and external rotations. The anterior cruciate ligament then was cut and the same procedure was repeated. Transection of the ligament increased joint laxity for all types of rotation. The responsiveness of the neurons was not changed significantly by cutting the ligament (p > 0.05). Therefore, capsule afferents continue to behave normally in joints in which the anterior cruciate ligament has been transected. 

TI: Quantitative analysis of dorsal horn cell receptive fields following limited deafferentation-AU: Koerber-HR; Brown-PB-AD: Department of Neurobiology, University of Pittsburgh School of Medicine, Pennsylvania 15261, USA.-SO: J-Neurophysiol. 1995 Nov; 74(5): 2065-76

AB: 1. To test the hypothesis that subtotal deafferentation of dorsal horn cells can stimulate plastic changes in their receptive fields (RFs), diffuse deafferentation of the cat hindlimb dorsal horn was produced by transection of L7 or L6 and L7 dorsal roots. The following single-unit cutaneous low-threshold mechanoreceptor RF properties were compared between operated and control dorsal horns: 1) distance of RF center from tips of toes, 2) RF length-width ratio; and 3) RF area. 2. In both L7 and L6-L7 rhizotomized animals there was an increased incidence of silent electrode tracks in the most deafferented portion of the hindlimb map (the foot and toe representation). In the rhizotomized L6-L7 animals, there was also an increased incidence of symmetrically placed tracks in deafferented and control dorsal horns, in which cell RFs had no mirror-symmetrical components. In addition, cells in the lateral half of the L6 and L7 dorsal horns exhibited a proximal shift in the location of their RFs. In the rhizotomized L7 animals there was a distal shift of RFs in the L5 segment at long survival times. RFs had lower length-width ratios in L5 and L6 at short survival times and in L6 at long survival times. 3. In intact preparations, dorsal horn cells normally respond to inputs via single or small numbers of low-threshold cutaneous mechanoreceptors. Because these rhizotomies do not remove all inputs from any given area of skin, the deafferentations would produce only patchy loss of input from individual receptors. Therefore observed changes cannot be accounted for entirely by loss of afferent input, suggesting that some reorganization of dorsal horn cell RFs occurred. We conclude that the threshold stimulus for plastic change is less than total deafferentation of dorsal horn cells. At least some of the mechanisms underlying these changes may be active in normal animals in the maintenance of the somatotopic map or in conditioning. 

TI: Responses of mechanosensitive afferents to manipulation of the lumbar facet in the cat.-AU: Pickar-JG; McLain-RF-AD: Department of Anatomy and Physiology, Kansas State University, Manhattan, USA.-SO: Spine. 1995 Nov 15; 20(22): 2379-85-ISSN: 0362-2436

AB: STUDY DESIGN. The response of mechanosensitive afferent nerve endings in the lumbar spine to manipulation of a lumbar facet isolated using a unique surgical approach was studied in anesthetized adult cats. OBJECTIVES. To characterize sensory nerve endings in the lumbar spine with respect to their receptive field and conduction velocity and to assess their response to facet joint motion. SUMMARY OF BACKGROUND DATA. Previous studies have identified the presence of encapsulated endings in normal human facet capsules and have documented the presence of mechanosensitive units responsive to spinal loading. Previous neurophysiologic studies have used preparations that stripped all paraspinous musculature away from the field to expose the facets and lamina. METHODS. A unique hemilaminectomy approach was developed that permitted physiologic loading of the lumbar facet without disturbing its overlying musculature. Recordings of single unit afferent activity were made from fine filaments teased from the L6 dorsal root. Response to L5-L6 facet motion was studied by applying cranial, craniomedial, and medial distractive forces and lateral compressive forces to the facet joint. RESULTS. Single unit recordings were obtained from 16 afferents with receptive fields in the lumbar spine. Seven of 16 afferents had receptive fields in or near the facet, and the remaining nine afferents had receptive fields in paraspinal tissues some distance from the facet joint. There were nine Group II afferents, three Group IV, and four unclassified afferents. The majority of endings responded in a graded fashion relative to the direction of force applied. CONCLUSIONS. Mechanosensitive endings in the lumbar spine show graded sensitivity to the direction of facet manipulation. These Group III and IV afferents can reside some distance from the facet joint and remain sensitive to facet motion.

TI: Function of the glenohumeral ligaments in active stabilisation of the shoulder joint.-AU: Jerosch-J; Steinbeck-J; Clahsen-H; Schmitz-Nahrath-M; Grosse-Hackmann-A-AD: Orthopaedic Department, Westfalische Wilhelms-University Munster, Germany.-SO: Knee-Surg-Sports-Traumatol-Arthrosc. 1993; 1(3-4): 152-8-ISSN: 0942-2056

AB: The joint capsules and the glenohumeral ligaments of 12 human shoulder specimens were histologically investigated by light microscopy. Serial sections of 15 microns thickness were cut. The tissue was stained following the haematoxylin-eosin and van Giesson techniques. For specific identification of neural elements we made use of a special silver impregnation technique, described by Novotny, for staining axons in peripheral nerves. Axons of different diameters ranging from 0.2 microns to 70 microns were discovered within the ligaments. Close to the humeral site we found small nerves forming neurovascular bundles. Within their connective tissue sheaths, the axons exhibited a serpentine configuration, which may give extra length and may allow stretching of the nerve during motion. Most of the axons discovered were located in the subsynovial layer of the ligaments. In general the diameter of these subsynovial axons did not exceed 10 microns. In addition to these axonal structures, we detected nerve endings which can be classified according to Freeman and Wyke as type II mechanoreceptors (Pacinian corpuscles). These mechanoreceptors had a diameter of approximately 150 microns. They were also positioned directly beneath the synovial membrane and close to the humeral site of insertion of the ligaments. Clinical significance: The described neural structures in the glenohumeral ligaments are of particular clinical importance in the light of the high incidence of recurrent shoulder dislocation and concomitant Bankart lesions. The mechanoreceptors located in the glenohumeral ligaments may control the stabilising shoulder musculature. On this premise, rupture or detachment of these ligaments will lead to a loss of a feedback mechanism.

TI: Does the glenohumeral joint capsule have proprioceptive capability?-AU: Jerosch-J; Castro-WH; Halm-H; Drescher-H-AD: Orthopedic Department, Westfalische Wilhelms University, Munster, Germany.-SO: Knee-Surg-Sports-Traumatol-Arthrosc. 1993; 1(2): 80-4-ISSN: 0942-2056

AB: We performed a clinical study examining 60 volunteers with stable shoulder joints randomized to two groups. In group 1 we injected 5 ml lidocaine intra-articularly. In group 2 we injected 5 ml saline with 5 ml contrast dye the same way. After the injection we measured the amount of passive anteroposterior translation that occurred during anterior and posterior drawer tests and the amount of inferior subluxation during downward stress. We documented the extent of the passive glenohumeral translation using ultrasound. We had no complications related to the intra-articular injection or to the stability measurement. After the injection neither group had significant pain, and the patients were not apprehensive about the ensuing stability test. In group 1 (lidocaine) anteroposterior translation of 13.2 +/- 6.3 mm was seen in the anterior and posterior drawer test, whereas in group 2 (no lidocaine) the anteroposterior translation was only 6.8 +/- 3.2 mm. The difference between the two groups was statistically significant (P < 0.05). With downward stress during the sulcus test the distance between the acromion and the humeral head increased by 5.6 mm (+/- 3.2) in group 1 and by 2.7 mm (+/- 2.1) in group 2. This difference was also statistically significant (P < 0.05). Clinical consequences: Taking our preliminary findings into account, the capsule of the glenohumeral joint seems to have proprioceptive capability. Nerve fibres and mechanoreceptors seem to be localized in the capsule tissue, being part of a physiological feedback mechanism. If our conclusions proprioceptive capability. Nerve fibres and mechanoreceptors seem to be localized in the capsule tissue, being part of a physiological feedback mechanism.MESH: Adolescence-; Adult-; Aged-; Anesthetics,-Local; Injections,-Intra-Articular; Joint-Capsule-drug-effects; Joint-Capsule-innervation; Lidocaine-; Middle-Age; Muscle-Contraction-physiology; Muscle,-Skeletal-innervation; Muscle,-Skeletal-physiology; roprioception-drug-effects; Proprioception-physiology; Shoulder-Joint-innervation; Shoulder-Joint-ltrasonography

TI: Presence of neuroreceptors in normal and diseased temporo-mandibular joints.-AU: Favia-G; Maiorano-E-AD: Dental Clinic, University of Bari.-SO: Boll-Soc-Ital-Biol-Sper. 1995 Jul-Aug; 71(7-8): 205-12-ISSN: 0037-8771

AB: An immunohistochemical study was performed on the articular disk and periarticular tissues of the temporo-mandibular joint (TMJ) in order to ascertain the presence of neuroreceptors (NRec) in these sites. The study was carried out with the APAAP technique on tissue samples obtained from 10 subjects without known TMJ disease and from 5 patients with severe TMJ arthritis or arthrosis. The antibodies used were directed against the following antigens: Gliofibrillary Acidic Protein (GFAP), Leu-7, Myelin Basic Protein (MBP), Neurofilaments 68 kD (NF), Neuron Specific Enolase (NSE), S-100 protein (S-100) and Synaptophysin (SYN). This study revealed that Ruffini's-like, Pacini's-like and Golgi's-like receptors can be demonstrated in TMJ periarticular tissues and that free nervous endings are present in the subsynovial but not within the articular disk. In the latter, elongated cytoplasmic processes of chondrocytes demonstrated strong S-100 immunoreactivity but they were unreactive with all other antibodies. These cytoplasmic processes were more abundant and thicker in the samples obtained from patients with diseased TMJ. The results of this study confirm that different NRec are detectable in TMJ periarticular tissues but they are absent within the articular disk. In the latter site, only chondrocytic processes are evident, especially in diseased TMJ, and they might have been confused with nervous endings in previous morphological studies. Nevertheless the absence of immunoreactivity for NF, NSE and SYN proves that they are not of neural origin.

TI: Peripheral regeneration and central sprouting of sensory neurone axons in Aplysia californica following nerve injury.-AU: Steffensen-I; Dulin-MF; Walters-ET; Morris-CE-AD: Neurosciences, Loeb Institute, University of Ottawa, Ontario, Canada.-SO: J-Exp-Biol. 1995 Oct; 198 ( Pt 10): 2067-78-ISSN: 0022-0949

AB: Morphological methods were used to examine injury-induced growth of peripheral and central axons of nociceptive mechanosensory neurones in the ventrocaudal (VC) clusters of the pleural ganglia of Aplysia californica. Pedal nerve crush transected all axons in the nerve while leaving the overlying sheath largely intact. Immunohistochemical staining was performed with an antibody to a sensory-neurone-specific peptide, sensorin-A. Following bilateral crush of pedal nerve p9, which innervates the tail, sensorin-A immunofluorescence was lost distal to the crush site within 2 days. Fine immunopositive fibres began to invade the crush region within 5 days. These fibres arborized in the crush region and gradually extended down the crushed nerve. Immunopositive fibres were found near the tail within 3 weeks. Similar results were obtained after injecting individual sensory neurone somata in the tail/p9 region of the VC cluster with biocytin. Biocytin injections and horseradish peroxidase injections 3 weeks after ipsilateral pedal nerve crush revealed new fibres projecting rostrally from the tail/p9 region of the VC cluster and entering the pleural-cerebral and pleural-abdominal connectives. Such projections were never observed in control, uncrushed preparations. These results demonstrate that nerve injury triggers extensive growth of both peripheral and central processes of the VC sensory neurones.

 TI: Perspectives on the role of afferent signals in control of motor neuroprostheses.-AU: Johnson-KO; Popovic-D; Riso-RR; Koris-M; Van-Doren-C; Kantor-C-AD: Krieger Mind/Brain Institute, Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.-SO: Med-Eng-Phys. 1995 Oct; 17(7): 481-96-ISSN: 1350-4533

AB: K.O. Johnson reviews the architecture and low level neural mechanisms by which the external environment is transduced and encoded into the neural system, summarizing work that correlates neurophysiological and psychophysical testing with isolation of sensory components. The slowly adapting Type I afferent system is responsible for form and texture perception; the rapidly adapting afferent system is responsible for motion perception; and the Pacinian corpuscle system is responsible for vibratory sensation. R.R. Riso reviews the current level of understanding of the major factors to be considered in the design of a functional neuromuscular stimulation (FNS) grasp controller that uses cutaneous sensory feedback to detect slip. The elegant natural control scheme that matches the ratio of grip and lift forces to frictional conditions provides a model for implementing a slip-based control algorithm. D. Popovic discusses the possible use of recordings from more proximal peripheral nerves to determine needed information for synthesis of locomotion. The discussion is illustrated with an animal model where rule-based closed-loop control is used for the ankle joint during treadmill locomotion. Neural signals from the tibial and superficial peroneal nerves were employed to substitute for missing afferent input from cutaneous and proprioceptive sensors. The feasibility of more invasive intraneural electrodes for distinguishing sensory from motor information in mixed nerves is considered. M. Koris raises surgical and functional issues relevant to developing clinical FNS systems. C. Van Doren suggests alternative neurophysiological and engineering approaches.

TI: Genetic approaches to mechanosensory transduction.-AU: Kernan-M; Zuker-C-AD: Department of Neurobiology and Behavior, State University of New York at -Stony Brook 11794-5230, USA.-SO: Curr-Opin-Neurobiol. 1995 Aug; 5(4): 443-8-ISSN: 0959-4388

AB: Genetic approaches in several organisms provide the means of solving a previously intractable problem: characterizing the molecular foundations of the mechanical senses. In nematode mechanosensory cells, members of a novel class of epithelial ion channel subunits have been implicated as components of a mechanically gated channel. In insect mechanosensory bristles, mutations specifically defective in mechanoreceptor potentials have been identified. And in bacteria, a stretch-activated channel has been molecularly characterized for the first time. Although mechanosensitivity can be a property of an isolated channel, sensory transduction in eukaryotic mechanosensory cells probably requires the interaction of several membrane and cytoskeletal components. 

TI: Mechanical stimulation increases intracellular calcium concentration in nodose sensory neurons.-AU: Sharma-RV; Chapleau-MW; Hajduczok-G; Wachtel-RE; Waite-LJ; Bhalla-RC; Abboud-FM-AD: Department of Anatomy, University of Iowa, College of Medicine, Iowa City, USA.-SO: Neuroscience. 1995 May; 66(2): 433-41-ISSN: 0306-4522

AB: The cellular mechanisms involved in activation of mechanosensitive visceral sensory nerves are poorly understood. The major goal of this study was to determine the effect of mechanical stimulation on intracellular calcium concentration ([Ca2+]i) using nodose sensory neurons grown in culture. Primary cultures of nodose sensory neurons were prepared by enzymatic dispersion from nodose ganglia of 4-8 week old Sprague-Dawley rats. Whole cell [Ca2+]i was measured by a microscopic digital image analysis system in fura-2 loaded single neurons. Brief mechanical stimulation of individual nodose sensory neurons was achieved by deformation of the cell surface with a glass micropipette. In 31 of 50 neurons (62%), mechanical stimulation increased [Ca2+]i from 125 +/- 8 to 763 +/- 89 nM measured approximately 10 s after stimulation. [Ca2+]i then declined gradually, returning to near basal levels over a period of minutes. [Ca2+]i failed to increase after mechanical stimulation in the remaining 19 neurons. The mechanically-induced rise in [Ca2+]i was essentially abolished after the neurons were incubated for 5-10 min in zero Ca2+ buffer (n = 7) or after addition of gadolinium (10 microM), a blocker of stretch-activated ion channels (n = 5). The effect of gadolinium was reversed after removal of gadolinium. The results indicate that: (1) mechanical stretch increases [Ca2+]i in a subpopulation of nodose sensory neurons in culture, and (2) the stretch-induced increase in [Ca2+]i is dependent on influx of Ca2+ from extracellular fluid and is reversibly blocked by gadolinium. The findings suggest that opening of stretch-activated ion channels in response to mechanical deformation leads to an increase in Ca2+ concentration in visceral sensory neurons.

TI: Eye movements in normal subjects induced by vibratory activation of neck muscle proprioceptors.-AU: Han-Y; Lennerstrand-G-AD: Department of Ophthalmology, Karolinska Institute, Huddinge University Hospital, Sweden.-SO: Acta-Ophthalmol-Scand. 1995 Oct; 73(5): 414-6-ISSN: 1395-3907

AB: Versional eye movements, induced by neck muscle vibration at 70 Hz in 8 normal subjects, were recorded with infrared reflection technique in each eye separately with one eye fixating a target and the other covered. The direction of eye movements was horizontal when the sternocleidomastoid muscle on one side of the neck and the splenius on the other side were activated, and downward when both splenii muscles were vibrated. The direction was the same as that of the illusory movements of the target also induced by the vibration. These findings would imply that the proprioceptive messages originating in the neck muscles are processed together with visual information of eye position in determining gaze direction.

TI: Egocentric visual target position and velocity coding: role of ocular muscle proprioception.-AU: Gauthier-GM; Vercher-JL; Blouin-J-AD: Laboratoire de Controles Sensorimoteurs, Universite de Provence, Marseille, France.-SO: Ann-Biomed-Eng. 1995 Jul-Aug; 23(4): 423-35-ISSN: 0090-6964

AB: Limited knowledge is available regarding the processes by which the brain codes the velocity of visual targets with respect to the observer. Two models have been previously proposed to describe the visual target localization mechanism. Both assume that the necessary information is derived from the coding of the position of the eye in the orbit, either through a copy of the muscular activation (out flow model) or through eye muscle proprioception (in flow model). Eye velocity coding might be derived from velocity sensitive ocular muscle proprioceptors or from position coding signals through differentiation. We used techniques based on manual pointing and manual tracking of visual target, combined with passive deviation of one covered eye, to demonstrate that ocular muscle proprioception is involved in (i) eye-in-head position coding, hence in target localization function; (ii) long-term maintenance of ocular alignment (phoria); and (iii) sensing of visual target velocity with respect to the head. These observations support other data now available, describing the processes by which the brain codes position and velocity of visual targets. Such findings might interest engineers in the field of robotics who are facing the problem of providing robots with the ability to sense object position and velocity in order to create an internal model of their working environment.

TI: Regulation of soleus muscle spindle sensitivity in decerebrate and spinal cats during postural and locomotor activities.-AU: Bennett-DJ; De-Serres-SJ; Stein-RB-AD: Department of Physiology, University of Alberta, Edmonton, Canada.-SO: J-Physiol-Lond. 1996 Sep 15; 495 ( Pt 3): 835-50-ISSN: 0022-3751

AB: 1. In order to study fusimotor control in reduced preparations, soleus muscle spindle afferents were recorded in premammillary decerebrate cats (n = 15) during crossed extensor reflexes and, after spinalization, during locomotion produced by either clonidine or L-beta-3,4-dihydroxyphenylalanine (L-DOPA). The soleus muscle was oscillated sinusoidally (0.25 mm, 4 Hz) and the afferent mean firing rate and modulation were calculated. An increase in firing rate was assumed to arise from activity in dynamic gamma-motoneurones (dynamic gamma-

drive) when associated with an increase in modulation to stretching, and in static gamma-motoneurones (static gamma-drive) when modulation decreased. 2. At rest in all preparations the firing rate and modulation in primary muscle spindle afferents were generally much higher than after de-efferentation (ventral root section), suggesting a predominant dynamic gamma-drive. Clonidine decreased and even eliminated this presumed resting gamma-drive in many afferents, both in the decerebrate (7 of 8) and the spinal (6 of 18) state. This effect on gamma-drive may account, at least in part, for its suppressive effect on spasticity in humans. 3. When locomotion commenced in clonidine-treated spinal cats, primary afferents generally fired with much higher mean rates (+121%) and lower sensitivities (-32%), suggesting a large increase in static gamma-drive (possibly accompanied by a small decrease in dynamic gamma-drive). These high rates were usually maintained tonically throughout the step cycle. However, a third of the afferents were silenced during locomotor contractions, and de-efferentation had no significant effect on their firing rates. Thus, for some spindles alpha-activity can occur without significant gamma-drive. 4. During locomotion in L-DOPA-treated spinal cats the inferred static gamma-drive only occurred phasically, coactivated with the EMG, though it could precede the EMG by 100-500 ms. In the flexion phase both the afferent rate and modulation were lower than before locomoton, suggesting a lack of effective gamma-drive. 5. Crossed extensor reflexes in decerebrate cats also produced a substantial increase in primary afferent firing rate (+187%) and decrease in sensitivity (-37%), again suggesting increased static gamma-drive (n = 18). This gamma-drive was largely independent of EMG activity and often occurred without alpha-activity. The mean firing rate of secondary muscle spindle afferents increased significantly during locomotion (with L-DOPA) and crossed extensor reflexes, again indicating increased static gamma-drive. Clonidine reduced or eliminated the gamma-drive in seven of eight afferents during crossed extensor reflexes. 6.

In conclusion, although there are some common features, such as a predominant static gamma-drive in all walking preparations, the pattern of static and dynamic gamma-drive is not closely linked to alpha-activity under the conditions studied. As well as gamma-drive without alpha-activity, we have shown for the first time that alpha-motoneurones can be activated without significant gamma-drive to many spindles during behavioural tasks.MESH: Action-Potentials-drug-effects; Action-Potentials-physiology; Afferent-Pathways-physiology; Afferent-Pathways-physiopathology; Cats-; Clonidine-pharmacology; Electrophysiology-; Levodopa-pharmacology; Motor-Activity-drug-effects; Motor-Activity-physiology; Motor-Neurons,-Gamma-drug-effects; Motor-Neurons,-Gamma-physiology; Muscle-Contraction-drug-effects; Muscle-Contraction-physiology; Muscle,-Skeletal-physiology; Posture-physiology; Sympatholytics-pharmacology

TI: Light microscopic observations of the contacts made between two spindle afferent types and alpha-motoneurons in the cat trigeminal motor nucleus.-AU: Yabuta-NH; Yasuda-K; Nagase-Y; Yoshida-A; Fukunishi-Y; Shigenaga-Y-AD: Department of Oral Anatomy, Osaka University Faculty of Dentistry, Japan.-SO: J-Comp-Neurol. 1996 Oct 21; 374(3): 436-50-ISSN: 0021-9967

AB: Previous studies indicate that cat jaw-muscle spindle afferents can be divided into two types (type I and II) on the basis of their axonal trajectories. The present study examined the relationship between spindle afferent fibers and their target masseter alpha-motoneurons in the cat by using the intracellular horseradish peroxidase (HRP) injection technique, and provided several new findings on the synaptic organization generated between the two. Five type I afferent fiber-motoneuron pairs and nine type II afferent-motoneuron pairs were well stained with HRP. The following conclusions were drawn: 1) A motoneuron received contacts from only one collateral of any given spindle afferent. 2) The number of contacts made between an afferent and a motoneuron ranged from one to three. 3) The contacts made by a spindle afferent were on the same dendrite or dendrites branching from the same primary dendrite. 4) The vast majority of the contacts made by an afferent on a motoneuron were distributed in the dendritic tree within 600 microns from the soma, i.e., in the proximal three fourths of the dendritic tree. The differences observed between the two afferent types were as follows. First, type II afferent terminals made contacts on more distal dendrites of the motoneurons than did type I afferent terminals. Second, the contacts made between a type I afferent and a motoneuron were clustered together, but those made between a type II afferent and a motoneuron were widely dispersed. The present results provided the general rules of synaptic contacts between the spindle afferents and masseter alpha-motoneurons, and demonstrated that the spatial distribution of synaptic contacts on the dendritic tree was different between type I and type II afferents.

TI: Ensemble coding of muscle stretches in afferent populations containing different types of muscle afferents.-AU: Bergenheim-M; Johansson-H; Pedersen-J; Ohberg-F; Sjolander-P-AD: Department of Work Physiology and Technology, National Institute for Working Life, Umea, Sweden.-SO: Brain-Res. 1996 Sep 23; 734(1-2): 157-66-ISSN: 0006-8993

AB: Ensemble coding of simple mechanical stimuli (small sinusoidal stretches) was studied in simultaneously recorded mixed ensembles of primary- and secondary muscle spindle afferents (MSAs), and Golgi tendon organ (GTO) afferents recorded from L7-S1 dorsal root filaments. The experiments were made on 48 recorded afferents (29 primary MSAs, 6 secondary MSAs and 13 GTO afferents) in chloralose anaesthetised cats. For the analyses, we used a combination of principal component analysis and algorithms for quantification of stimulus discrimination. Mixed ensembles of primary- and secondary MSAs, and GTO afferents, discriminated significantly better between different muscle stretches than ensembles of only one or two types of these afferents. All kinds of ensembles showed a successive increase in discriminative ability with increased ensemble size and this ability seemed to level at larger populations. However, the increase in discriminative ability was significantly greater for the mixed ensembles. It is hypothesised that the main reason for the greater discriminative ability achieved by mixed ensembles, might be that the variation in response profiles (sensitivity tuning) among the individual afferents of the mixed ensemble will be larger than that for ensembles of only one type of afferent. Finally, the results in the present study give experimental support to some of the teleological arguments in favour of the ensemble coding theory.

TI: Motor adaptation to Coriolis force perturbations of reaching movements: endpoint but not trajectory adaptation transfers to the nonexposed arm.-AU: Dizio-P; Lackner-JR-AD: Ashton Graybiel Spatial Orientation Laboratory, Brandeis University, Waltham, Massachusetts 02254-9110, USA.-SO: J-Neurophysiol. 1995 Oct; 74(4): 1787-92-ISSN: 0022-3077

AB: 1. Reaching movements made in a rotating room generate Coriolis forces that are directly proportional to the cross product of the room's angular velocity and the arm's linear velocity. Such Coriolis forces are inertial forces not involving mechanical contact with the arm. 2. We measured the trajectories of arm movements made in darkness to a visual target that was extinguished at the onset of each reach. Prerotation subjects pointed with both the right and left arms in alternating sets of eight movements. During rotation at 10 rpm, the subjects reached only with the right arm. Postrotation, the subjects pointed with the left and right arms, starting with the left, in alternating sets of eight movements. 3. The initial perrotary reaching movements of the right arm were highly deviated both in movement path and endpoint relative to the prerotation reaches of the right arm. With additional movements, subjects rapidly regained straight movement paths and accurate endpoints despite the absence of visual or tactile feedback about reaching accuracy. The initial postrotation reaches of the left arm followed straight paths to the wrong endpoint. The initial postrotation reaches of the right arm had paths with mirror image curvature to the initial perrotation reaches of the right arm but went to the correct endpoint. 4. These observations are inconsistent with current equilibrium point models of movement control. Such theories predict accurate reaches under our experimental conditions. Our observations further show independent implementation of movement and posture, as evidenced by transfer of endpoint adaptation to the nonexposed arm without transfer of path adaptation. Endpoint control may occur at a relatively central stage that represents general constraints such as gravitoinertial force background or egocentric direction relative to both arms, and control of path may occur at a more peripheral stage that represents moments of inertia and muscle dynamics unique to each limb. 5. Endpoint and path adaptation occur depite the absence both of mechanical contact cues about the perturbing force and visual or tactile cues about movement accuracy. These findings point to the importance of muscle spindle signals, monitoring of motor commands, and possibly joint and tendon receptors in a detailed trajectory monitoring process. Muscle spindle primary and secondary afferent signals may differentially influence adaptation of movement shape and endpoint, respectively.

TI: Time-dependent fusimotor effects on the discharge of cat primary muscle spindle afferents induced by a long-lasting succinylcholine infusion.-AU: Schafer-SS; Schoppmeyer-MA-AD: Department of Neurophysiology (4230), Medical School of Hannover, Germany.-SO: Brain-Res. 1996 Feb 12; 709(1): 111-21-ISSN: 0006-8993

AB: The responses of 46 Ia afferents from the tibial anterior muscle of the cat to repetitive ramp-and-hold stretches were investigated under a succinylcholine (SCh) infusion of 120 micrograms.kg-1.min-1 lasting 15 to 25 min. It was possible to distinguish four consecutive phases of the effect of the SCh on the responsiveness of the Ia afferents. The first three of these four phases have already been described. We analysed in more detail the changes from Phase III to the end of Phase IV. Static fusimotor effects were dominant in the discharge patterns obtained during Phase III; dynamic fusimotor effects prevail at the end of Phase IV. Our observations were quantified by comparing the mean values of initial activity, final static value, dynamic response and slow receptor adaptation read from the discharge patterns obtained during Phase III with the mean values of the same parameters obtained from discharge patterns from the end of Phase IV: the two mean values were significantly different for each of the four measurements. This change from Phase III to the end of Phase IV is highly specific for each spindle. To demonstrate this spindle specificity, discharge patterns were selected from among those produced by each Ia afferent in Phase III and at the end of Phase IV. Each of these discharge patterns was assigned to one of six categories. Category I displays purely dynamic fusimotor effects and Category VI purely static fusimotor effects. Categories II, IV and V display combinations of static and dynamic fusimotor effects with an increasing admixture of static fusimotor effects. The spindle-specific change from Phase III to the end of Phase IV is defined in terms of the specific degree of change from a higher-number to a lower-number category in the case of each of the 46 Ia afferents. In the discussion a combination of activity by the two nuclear bag fibres of a spindle is deduced from the specific discharge pattern of each category. The conclusion from these considerations is that results obtained from the adminisration of SCh have to be interpreted with great caution in making any statement about the existence of a dynamic bag1 fibre in a spindle.

TI: Activity of the intercostal muscle spindle afferents in the lower thoracic segments during spontaneous breathing in the cat.-AU: Hirai-N; Ichikawa-T; Ichikawa-T; Miyashita-M-AD: Department of Physiology, Kyorin University School of Medicine, Tokyo, -Japan.-SO: Neurosci-Res. 1996 Jul; 25(3): 301-4-ISSN: 0168-0102

AB: Intraaxonal recordings of 33 spindle afferents from the inspiratory (n = 8) and expiratory (n = 25) intercostal muscles in the lower thoracic segment (T9-11), were made during spontaneous breathing in the anesthetized cat. All of them showed respiration-related activity. However, only three spindle afferents (one from the inspiratory and two from the expiratory intercostal muscles) showed higher firing frequency during the active contraction phase of the receptor-bearing muscle. The remaining 30 spindle afferents (seven from the inspiratory and 23 from the expiratory muscles) showed the maximum firing discharge during the passive stretch phase of the parent muscles. On the other hand, in the middle thoracic segments (T6-7), five of six spindle afferents from the inspiratory muscles and four of nine spindle afferents from the expiratory muscles showed maximum firing rate during parent muscle contraction in agreement with previous study. These results suggest that the spindle activity in the lower thoracic segments is dominated by muscle length changes, whereas that in the middle thoracic segments is largely via the fusimotor pathway.

TI: Group I extensor afferents evoke disynaptic EPSPs in cat hindlimb extensor motorneurones during fictive locomotion.-AU: Angel-MJ; Guertin-P; Jimenez-T; McCrea-DA-AD: Department of Physiology, Faculty of Medicine, University of Manitoba, -Winnipeg, Canada.-SO: J-Physiol-Lond. 1996 Aug 1; 494 ( Pt 3): 851-61-ISSN: 0022-3751

AB: 1. Intracellular recording from extensor motoneurones in paralysed decerebrate cats was used to examine the distribution of short-latency non-monosynaptic excitation by group I afferents during fictive locomotion produced by stimulation of the mesencephalic locomotor region (MLR). 2. During the extension but not the flexion phase of fictive locomotion, stimulation of ankle extensor nerves at 1.2-2.0 times threshold evoked excitatory postsynaptic potentials (EPSPs) in motoneurones innervating hip, knee and ankle extensors. Disynaptic EPSPs were also evoked by selective activation of group Ia muscle spindle afferents by muscle stretch. 3. The central latencies of these group I-evoked EPSPs (mean, 1.55 ms) suggest their mediation by a disynaptic pathway with a single interneurone interposed between extensor group I afferents and extensor motoneurones. Disynaptic EPSPs were also evoked during periods of spontaneous locomotion following the cessation of MLR stimulation. 4. Hip extensor motoneurones received disynaptic EPSPs during extension following stimulation of both homonymous and ankle extensor nerves. Stimulation of hip extensor nerves did not evoke disynaptic EPSPs in ankle extensor motoneurones. 5. The appearance of disynaptic EPSPs during extension appears to result from cyclic disinhibition of an unidentified population of excitatory spinal interneurones and not postsynaptic voltage-dependent conductances in motoneurones or phasic presynaptic inhibition of group I afferents during flexion. 6. The reorganization of group I reflexes during fictive locomotion includes the appearance of disynaptic excitation of hip, knee and ankle extensor motoneurones. This excitatory reflex is one of the mechanisms by which group I afferents can enhance extensor activity and increase force production during stance.

TI: A numerical simulation of muscle spindle ensemble encoding during planar movement of the human arm.AU: Wallace-KR; Kerr-GK-AD: University Laboratory of Physiology, University of Oxford, UK. -krw@motor.physiol.ox.ac.uk-SO: Biol-Cybern. 1996 Oct; 75(4): 339-50-ISSN: 0340-1200

AB: We address the issue of what proprioceptive information, regarding movement of the human arm, may be provided to the central nervous system by proprioceptors located within muscles of this limb. To accomplish this we developed a numerical simulation which could provide estimates of the length regimes experienced by a set of model receptors located within some of the principal muscles of the human arm during planar movement of this limb. These receptors were assumed to have characteristics analogous to those associated with a simple model of muscle spindle signalling of movement. To this end each spindle had proprioceptive 'channels' associated with it. These corresponded to primary and secondary spindle afferent fibers which could provide independent afferent output regarding the parent muscle the spindle monitored. The angles of the shoulder and elbow joints attained by subjects performing a task requiring movement of the right arm in a horizontal plane to a static visual target were recorded. For this angular data the lengths and rates of change of lengths experienced by muscle fascicles, and hence the model spindles, during movement were calculated by means of the numerical simulation. The discharge rates of the simulated spindles during the movement were calculated to derive a measure of the depth of modulation, induced by the movement, for each spindle. These values were then summed for all spindles to provide a first-order approximation of spindle ensemble coding of the movement. Significant correlations (P < 0.0001, Spearman's rank order) were found between the resulting ensemble encodings and, in order of significance, the angular velocity of the shoulder joint (rS = 0.945), the tangential velocity of the hand (rS = 0.942), and the angular velocity of the elbow joint (rS = 0.917). Correlations between the angular positions of the shoulder (rS = -0.623) and elbow (rS = 0.628) were lower. These findings indicate that the ensemble profiles of the simulated muscle spindles, encode information regarding kiematic parameters of movements related to both intrinsic and extrinsic coordinate systems. This suggests that motor structures capable of deriving such an ensemble encoding would be in a position to perform the sensory-motor transformations between intrinsic and extrinsic frames of reference necessary for controlling movements planned in extrinsic coordinates. 

TI: Pulsatile motor output in human finger movements is not dependent on the stretch reflex.AU: Wessberg-J; Vallbo-AB-AD: Department of Physiology, Goteborg University, Goteborg, Sweden. -wessberg@physiol.gu.se-SO: J-Physiol-Lond. 1996 Jun 15; 493 ( Pt 3): 895-908-ISSN: 0022-3751

AB: 1. Stretch perturbations were delivered during slow voluntary finger movements with the aim of exploring the role of the stretch reflex in generating the 8-10 Hz discontinuities that characterize these movements. Afferent activity from muscle spindle primary endings in the finger extensor muscles was recorded from the radial nerve, along with the EMG activity of these muscles, and kinematics of the relevant metacarpo-phalangeal joint. 2. Perturbations elicited a distinct response from the muscle spindles appearing at the recording electrode after 13 ms, and weak reflex responses from the muscle with peak-values at 53 and 63 ms during flexion and extension, respectively. 3. The time relations between kinematics, spindle firing and modulations of EMG activity elicited by the perturbations were compared with those of the self-generated discontinuities. These analyses indicate that stretch reflex mechanisms cannot account for the modulations of EMG activity that give rise to successive 8-10 Hz discontinuities. 4. A comparison of the reflex responses to perturbations with the EMG modulations during self-generated movements indicates that the reflex was too weak to account for the pulsatile motor output during voluntary movements. 5. By inference it was concluded that the 8-10 Hz discontinuities during self-generated movements are probably generated by mechanisms within the central nervous system.

TI: Contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat step cycle.-AU: Hiebert-GW; Whelan-PJ; Prochazka-A; Pearson-KG-AD: Department of Physiology, University of Alberta, Edmonton, Canada.-SO: J-Neurophysiol. 1996 Mar; 75(3): 1126-37-ISSN: 0022-3077

AB: 1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion during walking. The hip flexor muscle iliopsoas (IP) and the ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL) were stretched or vibrated at various phases of the step cycle in spontaneously walking decerebrate cats. Changes in electromyogram amplitude, duration, and timing were then examined. The effects of electrically stimulating group I and II afferents in the nerves to TA and EDL also were examined. 2. Stretch of the individual flexor muscles (IP, TA, or EDL) during the stance phase reduced the duration of extensor activity and promoted the onset of flexor burst activity. The contralateral step cycle also was affected by the stretch, the duration of flexor activity being shortened and extensor activity occurring earlier. Therefore, stretch of the flexor muscles during the stance phase reset the locomotor rhythm to flexion ipsilaterally and extension contralaterally. 3. Results of electrically stimulating the afferents from the TA and EDL muscles suggested that different groups of afferents were responsible for the resetting of the step cycle. Stimulation of the TA nerve reset the locomotor step cycle when the stimulus intensity was in the group II range (2-5 xT). By contrast, stimulation of the EDL nerve generated strong resetting of the step cycle in the range of 1.2-1.4 xT, where primarily the group Ia afferents from the muscle spindles would be activated. 4. Vibration of IP or EDL during stance reduced the duration of the extensor activity by similar amounts to that produced by muscle stretch or by electrical stimulation of EDL at group Ia strengths. This suggests that the group Ia afferents from IP and EDL are capable of resetting the locomotor pattern generator. Vibration of TA did not affect the locomotor rhythm. 5. Stretch of IP or electrical stimulation of TA afferents (5 xT) durng the flexion phase did not change the duration of the flexor activity. Stimulation of the EDL nerve at 1.8-5 xT during flexion increased the duration of the flexor activity. In none of our preparations did we observe resetting to extension when the flexor afferents were activated during flexion. 6. We conclude that as the flexor muscles lengthen during the stance phase of gait, their spindle afferents (group Ia afferents for EDL and IP, group II afferents for TA) act to inhibit the spinal center generating extensor activity thus facilitating the initiation of swing.

TI: A comparative study of changes operated by sympathetic nervous system activation on spindle afferent discharge and on tonic vibration reflex in rabbit jaw muscles.-AU: Passatore-M; Deriu-F; Grassi-C; Roatta-S-AD: Department of Anatomy and Human Physiology, Faculty of Medicine, University of Turin, Italy.-SO: J-Auton-Nerv-Syst. 1996 Mar 7; 57(3): 163-7-ISSN: 0165-1838

AB: The effect of sympathetic activation on the spindle afferent response to vibratory stimuli eliciting the tonic vibration reflex in jaw closing muscles was studied in precollicularly decerebrate rabbits. Stimulation of the cervical sympathetic trunk, at frequencies within the physiologic range, consistently induced a decrease in spindle response to muscle vibration, which was often preceded by a transient enhancement. Spindle discharge was usually correlated with the EMG activity in the masseter muscle and the tension reflexly developed by jaw muscles. The changes in spindle response to vibration were superimposed on variations of the basal discharge which exhibited different patterns in the studied units, increases in the firing rate being more frequently observed. These effects were mimicked by close arterial injection of the selective alpha 1-adrenoceptor agonist phenylephrine. Data presented here suggest that sympathetically-induced modifications of the tonic vibration reflex are due to changes exerted on muscle spindle afferent information. 

TI: Control of grip force during restraint of an object held between finger and thumb: responses of muscle and joint afferents from the digits.-AU: Macefield-VG; Johansson-RSAD: Department of Physiology, Umea University, Sweden.SO: Exp-Brain-Res. 1996 Feb; 108(1): 172-84-ISSN: 0014-4819

AB: Pulling or pushing forces applied to an object gripped between finger and thumb excite tactile afferents in the digits in a manner awarding these afferents probable roles in triggering the reactive increases in grip force and in scaling the changes in grip force to the changes in applied load-force. In the present study we assessed the possible contributions from slowly adapting afferents supplying muscles involved in the generation of grip forces and from digital joint afferents. Impulses were recorded from single afferents via tungsten microelectrodes inserted percutaneously into the median or ulnar nerves of awake human subjects. The subject held a manipulandum with a precision grip between the receptor-related digit (index finger, middle finger, ring finger or thumb) and an opposing digit (thumb or index finger). Ramp-and-hold load forces of various amplitudes (0.5-2.0 N) and ramp rates (2-32 N/s) were delivered tangential to the parallel grip surfaces in both the distal (pulling) and the proximal (pushing) directions. Afferents from the long flexors of the digits (n = 19), regardless of their muscle-spindle or tendon-organ origin, did not respond to the load forces before the onset of the automatic grip response, even with the fastest ramp rates. Their peak discharge closely followed the peak rate of increase in grip force. During the hold phase of the load stimulus, the afferents sustained a tonic discharge. The discharge rates were significantly lower with proximally directed loads despite the mean grip-force being similar in the two directions. This disparity could be explained by the differing contributions of these muscles to the finger-tip forces necessary to restrain the manipulandum in the two directions. Most afferents from the short flexors of the digits (n = 17), including the lumbricals, dorsal interossei, opponens pollicis, and flexor pollicis brevis, did not respond at all, even with the fastest ramps. Furthermore, the ensemble pattern from the joint afferents (n = 6) revealed no significan encoding of changes in finger-tip forces before the onset of the increase in grip force. We conclude that mechanoreceptors in the flexors of the digits and in the interphalangeal joints cannot be awarded a significant role in triggering the automatic changes in grip force. Rather, their responses appeared to reflect the reactive forces generated by the muscles to restrain the object. Hence, it appears that tactile afferents of the skin in contact with the object are the only species of receptor in the hand capable of triggering and initially scaling an appropriate change in grip force in response to an imposed change in load force, but that muscle and joint afferents may provide information related to the reactive forces produced by the subject. 

TI: Morphological evidence for recurrent jaw-muscle spindle afferent feedback within the mesencephalic trigeminal nucleus.-AU: Luo-P; Dessem-D-AD: Department of Physiology, University of Maryland Dental School, Baltimore 21201-1586, USA.-SO: Brain-Res. 1996 Feb 26; 710(1-2): 260-4-ISSN: 0006-8993

AB: Horseradish peroxidase was injected into the jaw-elevator muscles of rats. Jaw-muscle spindle afferent axons were then intracellularly stained with biotinamide. Eleven intracellularly stained somata were closely apposed by intracellularly labeled spindle afferent boutons. Spindle afferent boutons closely apposed another 10 mesencephalic trigeminal nucleus (Ve) perikarya labeled from the jaw muscles. These results indicate that an anatomical substrate exists for recurrent feedback between jaw-muscle spindle afferents within Vme.

TI: Control of locomotion in the decerebrate cat.-AU: Whelan-PJ-AD: Department of Physiology, Faculty of Medicine, University of Alberta, -Edmonton, Canada. pwhelan@gpu.srv.ualberta.ca-SO: Prog-Neurobiol. 1996 Aug; 49(5): 481-515

AB: Many of the general concepts regarding the control of walking were described years ago by: Sherrington (1906) Integrative Actions of the Nervous System. Yale University Press: New Haven, CT; Sherrington (1910a) Remarks on the reflex mechanism of the step, Brain 33, 1-25; Sherrington (1910b) Flexor-reflex of the limb, crossed extension reflex, and reflex stepping and standing (cat and dog), J. Physiol. (Lond.) 40, 28-121; Sherrington (1931) Quantitative management of contraction in lowest level coordination, Brain 54, 1-28; Graham-Brown (1912) The intrinsic factors in the act of progression in the mammal, Proc. R. Soc. Lond. 84, 308-319; Graham-Brown (1914) On the nature of the fundamental activity of the nervous centres; together with an analysis of the conditioning of rhythmic activity in progression, and a theory of the evolution of function in the nervous system, J. Physiol. 49, 18-46; Graham-Brown (1915) On the activities of the central nervous system of the unborn foetus of the cat, with a discussion of the question whether progression (walking, etc.) is a 'learnt' complex, J. Physiol. 49, 208-215; Graham-Brown (1922) The physiology of stepping, J. Neur. Psychopathol. 3, 112-116. Only in recent years, however, have the mechanisms been analyzed in detail. Quite a few of these mechanisms have been described using the decerebrate cat. Locomotion is initiated in decerebrate cats by activation of the mesencephalic locomotor region (MLR) that activates the medial medullary reticular formation (MRF) which in turn projects axons to the spinal cord which descend within the ventrolateral funiculus (VLF). The MRF region regulates as well as initiates the stepping pattern and is thought to be involved in interlimb coordination. Afferent feedback from proprioceptors and exteroceptors can modify the ongoing locomotor pattern. Recently, the types of afferents responsible for signaling the stance to swing transition have been identified. A general rule states that if the limb is unloaded and the leg is extended, then swng will occur. The afferents that detect unloading of the limb are the Golgi tendon organs and stimulation of these afferents (at group I strengths) prolongs the stance phase in walking cats. The afferents that detect the extension of the leg have been found to be the length- and velocity-sensitive muscle afferents located in flexor muscles. Plasticity of locomotor systems is discussed briefly in this article. Descerebrate animals can adapt locomotor behaviors to respond to new environmental conditions. Oligosynaptic reflex pathways that control locomotion can be recalibrated after injury in a manner that appears to be functionally related to the recovery of the animal.MESH: Brain-Mapping; Brain-Stem-physiopathology; Cerebral-Decortication; Conditioning,-Operant-physiology; Extremities-physiopathology; Ferrets-physiology; Interneurons-physiology; Learning-physiology; Mesencephalon-physiopathology; Models,-Neurological; N-Methylaspartate-antagonists-and-inhibitors; N-Methylaspartate-pharmacology; Neuronal-Plasticity; Neurotransmitters-physiology; Posture-physiology; Reflex-physiology; Reticular-Formation-physiopathology; Running-physiology; Spinal-Cord-physiopathology; Walking-physiology

TI: A numerical simulation of muscle spindle ensemble encoding during planar AU: Wallace-KR; Kerr-GK-AD: University Laboratory of Physiology, University of Oxford, UK.-krw@motor.physiol.ox.ac.uk-SO: Biol-Cybern. 1996 Oct; 75(4): 339-50-ISSN: 0340-1200

AB: We address the issue of what proprioceptive information, regarding movement of the human arm, may be provided to the central nervous system by proprioceptors located within muscles of this limb. To accomplish this we developed a numerical simulation which could provide estimates of the length regimes experienced by a set of model receptors located within some of the principal muscles of the human arm during planar movement of this limb. These receptors were assumed to have characteristics analogous to those associated with a simple model of muscle spindle signalling of movement. To this end each spindle had proprioceptive 'channels' associated with it. These corresponded to primary and secondary spindle afferent fibers which could provide independent afferent output regarding the parent muscle the spindle monitored. The angles of the shoulder and elbow joints attained by subjects performing a task requiring movement of the right arm in a horizontal plane to a static visual target were recorded. For this angular data the lengths and rates of change of lengths experienced by muscle fascicles, and hence the model spindles, during movement were calculated by means of the numerical simulation. The discharge rates of the simulated spindles during the movement were calculated to derive a measure of the depth of modulation, induced by the movement, for each spindle. These values were then summed for all spindles to provide a first-order approximation of spindle ensemble coding of the movement. Significant correlations (P < 0.0001, Spearman's rank order) were found between the resulting ensemble encodings and, in order of significance, the angular velocity of the shoulder joint (rS = 0.945), the tangential velocity of the hand (rS = 0.942), and the angular velocity of the elbow joint (rS = 0.917). Correlations between the angular positions of the shoulder (rS = -0.623) and elbow (rS = 0.628) were lower. These findings indicate that the ensemble profiles of the simulated muscle spindles, encode information regarding kiematic parameters of movements related to both

intrinsic and extrinsic coordinate systems. This suggests that motor structures capable of deriving such an ensemble encoding would be in a position to perform the sensory-motor transformations between intrinsic and extrinsic frames of reference necessary for controlling movements planned in extrinsic coordinates. 

TI: Cardiorespiratory changes when balancing one's whole body on one leg with eyes closed.AU: Kita-I; Sakamoto-M; Arita-H-AD: Department of Exercise and Sport Science, Tokyo Metropolitan University, Japan.-SO: Jpn-J-Physiol. 1996 Apr; 46(2): 145-53-ISSN: 0021-521X

AB: Postural control system has been extensively studied in terms of somatic motor function, but little is known about its connection with human autonomic function. The purpose of this study was to determine the cardiorespiratory changes in response to the 3-min load that was performed by balancing one's whole body on one leg with eyes closed (SOLEC load) or eyes open (SOLEO load) in 11 healthy young subjects (5 males and 6 females, mean age 20.8 +/- 1.9 year). Blood pressure (BP), heart rate (HR), respiratory rate (RR), inspiratory and expiratory duration (Ti and Te), tidal volume (VT), and oxygen uptake (VO2) were measured before, during, and after the load. The SOLEC load produced significant increases in HR and systolic BP within 1 min. There were further increases in systolic and diastolic BP during the late period of the load. Metabolic rate (VO2) showed a gradual increase during the SOLEC load, indicating that the late responses would be partly due to metabolic alteration. The early responses are considered to be mediated neurally through the postural control system which receives the afferent inputs arising from vestibular system and from muscle proprioceptors of the leg. In contrast, SOLEO load caused small insignificant changes in BP, HR, VT, and VO2, suggesting that a visual input is essential for balancing a postural change. The balance test with eyes closed may have value in a clinical neurological rehabilitation setting. 

TI: Efferent neurons of the lateral line system and their innervation of lateral line branches in a euteleost and an osteoglossomorph.AU: Wagner-T; Schwartz-E-AD: Institut fur Tierphysiologie, Universitat Giessen, Germany.thomas.wagner@uni-tuebingen.de-SO: Anat-Embryol-Berl. 1996 Sep; 194(3): 271-8ISSN: 0340-2061

AB: The efferent neurons of the lateral line system of the euteleost Aplocheilus lineatus and the osteoglossomorph Pantodon buchholzi, both surface feeding fish, were examined by neuronal tract tracing. Besides horse-radish peroxidase, fluorescent dextrans were used as tracers to allow simultaneus visualization of projections from different lateral line branches. Labeled efferent neurons were found in nuclei situated in the medulla ventral of ventricle IV. This position resembles the octa-volateralis efferent nucleus of previous studies. The number of labeled cells in the efferent nucleus is low in both species. Most neurons were found ipsilaterally to the application site, some along the midline and only very few contralaterally. The size of efferent cells differs distinctly between Aplocheilus, possessing small cell-bodies (length 16.5 microm), and Pantodon, which has very large efferent cells (length 47.0 micron). Efferent axon bundles course rostrally in both species, leaving the brain at the level of the anterior lateral line nerve. Only Aplocheilus has in addition lateral axon bundles leaving the brain at the level of the posterior lateral line nerve. After application of one fluorescent tracer to the lateral ramus and a different fluorescent tracer to the superficial ophtalmic ramus in a given animal, double-labeling of efferent cells hardly ever occurs. If the neuromasts I and IV of the dorsal skull of Pantodon are applied with one fluorescent tracer each, approximately 10% of centrally labeled cells are double-labeled. Considering the results of double-labeling, the concept of a differential innervation of lateral line branches is supported and discussed. 

TI: Divergence of ventilatory responses to isometric contraction in anesthetized cats.-AU: Wilson-LB; Wall-PT; Pawelczyk-JA; Matsukawa-K-AD: Department of Physiology, College of Medicine, University of South Alabama, -Mobile 36688-0002, USA.-SO: Respir-Physiol. 1996 Jul; 104(2-3): 137-46-ISSN: 0034-5687

AB: The purpose of this study was to determine if the initial ventilatory and phrenic nerve responses to isometric contraction of the triceps surae muscle of anesthetized cats are influenced by the pattern of the contraction. To address this, three different types of muscle contraction were evoked: (1) a high tension, continuous tetanic (HT-CT) contraction; (2) a moderate tension, continuous tetanic (MT-CT) contraction; and (3) high tension, intermittent tetanic (HT-IT) contractions. The duration of each contraction period was 60 sec. The MT-CT and HT-IT contractions increased minute volume (VE; 19 +/- 4% and 15 +/- 5%, respectively) within the first 15 sec. These increases were the result of rises in breathing frequency and tidal volume. However, only the MT-CT contraction increased phrenic activity (pVE) in the first 15 sec. By contrast, ventilation and phrenic nerve activity failed to increase within the first 15 sec of the HT-CT contraction. If fact, 'tidal' phrenic activity (pVT; -14 +/- 5%) decreased during the first 5 sec, and there was a tendency for tidal volume (VT; -8 +/- 5%), VE (-8 +/- 6%), and pVE (-16 +/- 8%) to fall. These data suggest that stimulation of muscle afferent fibers by static contraction can

initially inhibit phrenic nerve activity, provided the activation is sustained and of sufficient intensity.

TI: Developmental adaptation of withdrawal reflexes to early alteration of peripheral innervation in the rat.AU: Holmberg-H; Schouenborg-J-AD: Department of Physiology and Neuroscience, University of Lund, Sweden. Hans.Holmberg@mphy.lu.se-SO: J-Physiol-Lond. 1996 Sep 1; 495 ( Pt 2): 399-409-ISSN: 0022-3751

AB: 1. In adult decerebrate spinal rats whose plantar nerves (PLN) had been transected at either postnatal day 1 (P1) or P21 the nociceptive withdrawal reflexes (NWR) of musculi extensor digitorum longus (EDL), peroneus longus (PER) and semitendinosus (ST) were characterized with respect to receptive field (RF) organization, magnitude and time course, using electromyography. Thermal (short CO2 laser pulses) and mechanical (calibrated pinch) stimulation were used. The innervation patterns in normal and lesioned adult rats were assessed by acute nerve lesions. 2. The spatial organization of the mean mechano- and thermonociceptive RFs of all the muscles studied was similar to normal in both P1- and P21-lesioned rats, although in some P21-lesioned rats atypical EDL RFs were encountered. 3. In P1-lesioned rats thermo-NWR of PER and EDL had normal magnitudes, while mechano-NWR were reduced. In P21-lesioned rats both thermo- and mechano-NWR of these muscles had reduced magnitudes. Except for thermo-NWR of ST in P1-lesioned rats, which were increased, NWR of ST had normal magnitudes in both P1- and P21-lesioned rats. The time course of thermonociceptive NWR of the muscles studied were near normal in both P1- and P21-lesioned rats. 4. Acute nerve lesions in adult P1-lesioned rts revealed an essentially abolished contribution to NWR from the PLN. Instead, the contribution to NWR from other hindpaw nerves, such as the superficial and deep peroneal nerves, was dramatically increased. By contrast, in P21-lesioned rats, the regenerated PLN contributed significantly to the NWR. 5. It is concluded that despite profound alterations of plantar hindpaw innervation induced by early PLN transection the cutaneous nociceptive input to NWR attained an essentially normal spatial organization. An experience-dependent mechanism is suggested to be instrumental in adapting the reflex connectivity to the peripheral innervation.MESH: Animals,-Newborn; Electromyography-; Hindlimb-innervation; Hindlimb-physiology; Muscle,-Skeletal-innervation; Muscle,-Skeletal-physiology; Nociceptors-physiology; Physical-Stimulation; Rats-; Rats,-Wistar; Skin-innervation; Skin-physiology

TI: Forearm training attenuates sympathetic responses to prolonged rhythmic forearm exercise.AU: Sinoway-L; Shenberger-J; Leaman-G; Zelis-R; Gray-K; Baily-R; Leuenberger-U-AD: Division of Cardiology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033, USA.-SO: J-Appl-Physiol. 1996 Oct; 81(4): 1778-84-ISSN: 8750-7587

AB: We previously demonstrated that nonfatiguing rhythmic forearm exercise at 25% maximal voluntary contraction (12 2-s contractions/min) evokes sympathoexcitation without significant engagement of metabolite-sensitive muscle afferents (B.A. Batman, J.C. Hardy, U.A. Leuenberger, M.B. Smith, Q.X. Yang and L.I. Sinoway. J. Appl. Physiol. 76: 1077-1081, 1994). This is in contrast to the sympathetic nervous system responses observed during fatiguing static forearm exercise where metabolite-sensitive afferents are the key determinants of sympathetic activation. In this report we examined whether forearm exercise training would attenuate sympathetic nervous system responses to rhythmic forearm exercise. We measured heart rate, mean arterial blood pressure (MAP), muscle sympathetic nerve activity (microneurography), plasma norepinephrine (NE), and NE spillover and clearance (tritiated NE kinetics) during nonfatiguing rhythmic forearm exercise before and after a 4-wk unilateral forearm training paradigm. Training had no effect on forearm mass, maximal voluntary contraction, or heart rate but did attenuate the increase in MAP (increase in MAP: from 15.2 +/- 1.8 before training to 11.4 +/- 1.4 mmHg after training; P < 0.017), muscle sympathetic nerve activity (increase in bursts: from 10.8 +/- 1.4 before training to 6.2 +/- 1.1 bursts/min after training; P < 0.030), and the NE spillover (increases in arterial spillover: from 1.3 +/- 0.2 before training to 0.6 +/- 0.2 nmol.min-1.m-2 after training, P < 0.014; increase in venous spillover: from 2.0 +/- 0.6 before training to 1.0 +/- 0.5 nmol.min-1.m-2 after training, P < 0.037) seen in response to exercise performed by the trained forearm. Thus forearm training reduces sympathetic responses during a nonfatiguing rhythmic handgrip paradigm that does not engage muscle metaboreceptors. We speculate that this effect is due to a conditioning-induced reduction in mechanically sensitive muscle afferent discharge. 

TI: Changes in airway resistance induced by nasal inhalation of cold dry, dry, or moist air in normal individuals.AU: Fontanari-P; Burnet-H; Zattara-Hartmann-MC; Jammes-Y-AD: Laboratoire de Physiopathologie Respiratoire Integree et Cellulaire, Centre National de la Recherche Scientifique 1630, Institut Jean Roche, Faculte de Medecine, Universite de la Mediterrannee, Marseille, France.-SO: J-Appl-Physiol. 1996 Oct; 81(4): 1739-43-ISSN: 8750-7587

AB: Nasopulmonary bronchomotor reflexes elicited by mechanical or irritant stimulation of the nose have been described in animals and asthmatic patients. However, few studies were devoted to the consequences of nasal breathing of cold and dry air or of only dry or only moist air on the bronchomotor control in normal individuals. The present study reported changes in interruption resistance (Rint) measured during eupneic breathing of moderately cold (-4 or -10 degrees C) and dry [0.3% relative humidity (RH)] air or of room air at 23 degrees C that is either dry (0.3% RH) or moist (97% RH). Nasal inhalation of cold (-4 degrees C) dry air or of only dry air significantly increased baseline Rint value (17 and 21%, respectively) throughout the 15-min test periods. The response to cold was significantly accentuated when the air temperature was lowered to -10 degrees C (42%). After nasal anesthesia or inhalation of a cholinergic antagonist, cold air did not induce a change in Rint. Nasal inhalation of moist room air had no effect. No Rint changes were measured during oral breathing of the three test agents. It is concluded that the activation of cold receptors or osmoreceptors in the nasal mucosa induces protective bronchoconstrictor responses in normal individuals.MESH: Administration,-Inhalation; Adult-; Airway-Resistance-drug-effects; Cholinergic-Antagonists-administration-and-dosage; Cholinergic-Antagonists-pharmacology; Forced-Expiratory-Volume; Mechanoreceptors-drug-effects; Mechanoreceptors-physiology; Middle-Age; Nasal-Mucosa-drug-effects; Nasal-Mucosa-physiology; Pharynx-drug-effects; Pharynx-physiology; Reference-Values; Reflex-drug-effects; Reflex-physiology; Vital-Capacity 

TI: Somatosensory evoked potentials following proprioceptive stimulation of finger in man.-AU: Mima-T; Terada-K; Maekawa-M; Nagamine-T; Ikeda-A; Shibasaki-H-AD: Department of Brain Pathophysiology, Kyoto University School of Medicine, -Japan.-SO: Exp-Brain-Res. 1996 Sep; 111(2): 233-45-ISSN: 0014-4819

AB: Brisk passive flexion of the proximal interphalangeal joint of the middle -finger, produced by using a newly devised instrument, elicited evoked potentials on the scalp. The present study carefully excluded the possible contribution of sensory modalities other than proprioception. The initial part of cortical response was a positive deflexion at the contralateral central area (P1 at 34.6 ms after the stimulus). This was followed by a midfrontal negative wave (N1 at 44.8 ms) and a clear positivity at the contralateral centroparietal area (P2 at 48.0 ms). The evoked responses persisted in spite of the abolition of cutaneous and joint afferents of the finger caused by ischemic anesthesia, but they were lost by ischemic anesthesia of the forearm. Thus, the cortical evoked responses obtained in this study most probably reflect muscle afferent inputs. The scalp distribution of P1 suggested that its cortical generator source was different from that of the N20-P20 components of evoked potentials to electrical median nerve stimulation. Brodmann areas 2 and 3a of human brain, which are known to receive deep receptor inputs, are the most plausible generator sites for the early components of the proprioception-related evoked responses. The amplitude of P2 was related to the velocity but not to the magnitude of movement. In conclusion, the present study established a method for recording the evoked responses to the brisk passive movement of the finger joint, which mainly reflect the dynamic aspects of proprioception mediated through muscle afferent. 

TI: Sensory nerve supply in the human subacromial bursa.-AU: Ide-K; Shirai-Y; Ito-H; Ito-H-AD: Department of Anatomy and Orthopaedic Surgery, Nippon Medical School, Tokyo, -Japan.-SO: J-Shoulder-Elbow-Surg. 1996 Sep-Oct; 5(5): 371-82-ISSN: 1058-2746

AB: The subacromial bursa is the major component of the subacromial gliding mechanism. The neural elements of the subacromial bursa obtained from specimens that underwent autopsy and surgery were investigated by the silver impregnation and immunohistochemical methods with antisera to substance P and calcitonin gene-related peptide; which are considered to be involved in nociceptive transmission, and protein gene product 9.5. Free nerve endings, Ruffini endings, Pacinian corpuscles, and two kinds of unclassified nerve endings were observed. Most of these receptors were observed of the roof side of the coracoacromial arch, which is exposed to stress because of the impingement. A delta and C fibers, thought to be nerve fibers of free nerve endings, were immunoreactive to substance P and calcitonin gene-related peptide. On the other hand, thick fibers thought to originate in encapsulated mechanoreceptors were not immunoreactive to substance P. The subacromial bursa receives nociceptive stimuli and proprioception and seems to regulate appropriate shoulder movement. 

TI: Ensemble coding of muscle stretches in afferent populations containing different types of muscle afferents.AU: Bergenheim-M; Johansson-H; Pedersen-J; Ohberg-F; Sjolander-P-AD: Department of Work Physiology and Technology, National Institute for Working -Life, Umea, Sweden.-SO: Brain-Res. 1996 Sep 23; 734(1-2): 157-66-ISSN: 0006-8993

AB: Ensemble coding of simple mechanical stimuli (small sinusoidal stretches) was studied in simultaneously recorded mixed ensembles of primary- and secondary muscle spindle afferents (MSAs), and Golgi tendon organ (GTO) afferents recorded from L7-S1 dorsal root filaments. The experiments were made on 48 recorded afferents (29 primary MSAs, 6 secondary MSAs and 13 GTO afferents) in chloralose anaesthetised cats. For the analyses, we used a combination of principal component analysis and algorithms for quantification of stimulus discrimination. Mixed ensembles of primary- and secondary MSAs, and GTO afferents, discriminated significantly better between different muscle stretches than ensembles of only one or two types of these afferents. All kinds of ensembles showed a successive increase in discriminative ability with increased ensemble size and this ability seemed to level at larger populations. However, the increase in discriminative ability was significantly greater for the mixed ensembles. It is hypothesised that the main reason for the greater discriminative ability achieved by mixed ensembles, might be that the variation in response profiles (sensitivity tuning) among the individual afferents of the mixed ensemble will be larger than that for ensembles of only one type of afferent. Finally, the results in the present study give experimental support to some of the teleological arguments in favour of the ensemble coding theory.

TI: Experimental trigeminal nerve injury.AU: Holland-GR-AD: Department of Cariology, Restorative Sciences and Endodontics, School of Dentistry, University of Michigan, Ann Arbor 48109-1078, USA.-SO: Crit-Rev-Oral-Biol-Med. 1996; 7(3): 237-58

AB: The successful reinnervation of peripheral targets after injury varies with the axonal population of the nerve that is injured and the extent of the dislocation of its central component from the peripheral endoneurial tube. Larger-diameter axons such as those supplying mechanoreceptors recover more readily than narrower axons such as those supplying taste. A complex, bi-directional interaction between lingual epithelium and sprouting nerve results in the redifferentiation of taste buds after denervation. Dentin and the dental pulp provide a strong attraction to sprouting nerves and will become reinnervated from collateral sources if recovery of the original innervation is blocked. The most effective repair technique for transected lingual nerves is one which brings the cut ends together rather than one that provides a temporary bridge. Injuries can result in cell death in the trigeminal ganglion but only if the injury is severe and recovery is prevented. Lesser damage results in chromatolysis and the increased expression of neuropeptides. All nerve injuries bring about changes in the trigeminal nucleus. These occur as changes in receptive field and the incidence of spontaneously active neurons, effects which are consistent with the unmasking of existing afferents. These functional changes are short-lived and reversible. Morphologically, nerve injury results in terminal degeneration in the nuclei and an increased expression of the c-Fos gene and some neuropeptides. Only a chronic constriction injury induces behavioral changes. The adult trigeminal system retains considerable plasticity that permits it to respond successfully to nerve injury. Much remains to be learned about this response, particularly of the trophic factors that control peripheral recovery and the central response to more severe injuries.MESH: Adult-; Axons-physiology; Axons-ultrastructure; Cell-Death; Cell-Differentiation; Cell-Nucleus-ultrastructure; Dental-Pulp-innervation; Dentin-innervation; Epithelium-innervation; Gene-Expression-Regulation; Genes,-fos-genetics; Lingual-Nerve-injuries; Lingual-Nerve-physiology; Lingual-Nerve-surgery; Mechanoreceptors-physiology; Nerve-Degeneration; Nerve-Regeneration; Neuronal-Plasticity; Neurons,-Afferent-pathology; Neuropeptides-genetics; Taste-Buds-ultrastructure; Tongue-innervation; Trigeminal-Ganglion-injuries; Trigeminal-Ganglion-pathology; Trigeminal-Nerve-physiology; Trigeminal-Nuclei-pathology; Wound-Healing 

TI: Coordination between palatal and laryngeal muscle activities in response to rebreathing and lung inflation.AU: Koizumi-H; Kogo-M; Matsuya-T-AD: First Department of Oral and Maxillofacial Surgery, Osaka University Faculty of Dentistry, Japan.-SO: Cleft-Palate-Craniofac-J. 1996 Nov; 33(6): 459-62-ISSN: 1055-665