Toshinori Hongo

Spatial patterns of reflex evoked by pressure stimulation of the foot pads in cats.

1. The spatial patterns of reflexes elicited by localized pressure stimulation of the foot skin were analysed by recording electromyographic activities of various hindlimb muscles or muscle nerve discharges in cats anaesthetized with sodium pentobarbitone. 2. Reflex discharges evoked by stimulation of the central pad occurred mainly in physiological toe extensors located in the foot. Stimulus‐response relationships of single motor units revealed characteristically wide ranges of graded response and recruitment. 3. Within the central pad, the strongest excitation was evoked from the central lobe and was distributed to extensors of all four toes. Excitation from the medial and the lateral lobes was usually asymmetrical and weaker in toe muscles of the stimulated side. It is suggested that the weakness was in part due to concomitant inhibition. 4. Stimulation of a toe pad caused marked suppression of central pad‐evoked activity of toe extensors with a highly specific spatial pattern. The inhibition was strongest in extensors of its own toe, and gradually weaker in the more distant toes. Weak excitation was occasionally evoked in extensors of the most medial or lateral toes, when the most lateral or the most medial toe‐pad, respectively, was stimulated. 5. A similar pattern of relfex to that from the toe pad was evoked from the claw base and the hairy toe dorsum of each digit. 6. Reflex effects, both inhibitory and excitatory, from the central and toe pads, claw bases and toe dorsum were maintained during prolonged stimuli, indicating that slowly adapting receptors contributed to these reflexes. 7. It is concluded that stimulation of localized skin areas of the foot, particularly the pads, evokes highly specialized reflexes, which may be important in controlling movements of individual digits.

Cerebellar projection and input organizations of the spinocerebellar tract arising from the central cervical nucleus in the cat

The central cervical nucleus (CCN) has now been identified as consisting of cells of origin of a spinocerebellar tract by the retrograde labeling technique using horseradish peroxidase2,6,10,14. Anatomically, the CCN has been recognized as a separate cell group from the surroundings, existing at C1-C4, and to receive dorsal root fibres mainly of the cervical segmentsZ,5,8,11-13. The present study has been undertaken to physiologically characterize this new spinocerebellar tract with respect to its input and output organizations. Adult cats anaesthetized with Nembutal (30 mg/kg, i.p., and an additional 5-20 mg/kg, i.v.), immobilized with gallamine triethiodide and artificially ventilated were used for experiments. A glass capillary microelectrode (2 M potassium citrate) was inserted into the region of CCN through the dorsal column at C2-C4 segments to record from neurones activated antidromically from the white matter of the cerebellar anterior lobe with a negative pulse (0.2 msec duration) of less than 200 FA. The criteria for antidromic nature of the excitation were the same as described previously 4. The ipsilateral (to recording side) C2-C8 dorsal roots, peripheral nerve branches of the C2-C4 dorsal rami, various forelimb nerves, and the bilateral eighth nerves and the medial longitudinal fasciculus(MLF)were stimulated to explore synaptic inputs to the recorded neurones. After experiments the sites of cell recording in the cord and of stimulation in the cerebellum were determined histologically (cf. ref. 4). Spinocerebellar tract neurones identified as above were encountered in the region 0.3-0.8 mm lateral f rom the midline and 2.5-3.8 mm deep from the dorsal surface of the C2-C4 segments, where the CCN was located. In the centre of this region, cerebellar stimulation often evoked compound, antidromic field potentials consisting of several unitary spikes, which recruited with increase of stimulus strength (Fig. l A), indicating the existence of a cluster of spinocerebellar neurones. The sites of spinocerebellar neurones recorded in one animal at C2 are shown on a representative transverse plane in Fig. lB. As this was the case, most neurones were situated in the

The same interneurones mediate inhibition of dorsal spinocerebellar tract cells and lumbar motoneurones in the cat.

The aim of the study was to investigate whether inhibition of dorsal spinocerebellar tract (d.s.c.t.) cells evoked from group I afferents is mediated by the same interneurones which mediate the non‐reciprocal inhibition of hind‐limb motoneurones. The origin of inhibition of d.s.c.t. cells from group I afferents was compared in intact preparations, after lesions of the dorsal funiculi (when it could only be mediated by lower lumbar interneurones) and after lesions of the lateral and ventral funiculi (when it would be expected to be evoked by upper lumbar interneurones). In all three preparations extensors were the most common source of inhibition, as in motoneurones. Lower lumbar interneurones inhibiting d.s.c.t. cells were found to be co‐excited by group I (Ia and/or Ib) and cutaneous and joint afferents, and by rubrospinal tract fibres, as are interneurones mediating inhibition of motoneurones. Co‐excitation by group I and rubrospinal fibres was also found for upper lumbar interneurones. I.p.s.p.s were evoked in hind‐limb motoneurones from within Clarkes column in cats with the dorsal funiculi cut between L4 and L5 segments; they were evoked at thresholds as low as 2 microA, i.e. by stimuli with very local actions. The latencies of these i.p.s.p.s were short enough to allow them to be evoked monosynaptically via axonal branches of the same interneurones which projected to Clarkes column. Correspondingly, i.p.s.p.s were evoked in d.s.c.t. cells from within motor nuclei in L7 segments; they were evoked at similarly low thresholds and with similar latencies. In confirmation of previous reports i.p.s.p.s of Ia origin evoked in d.s.c.t. cells were not found to be depressed by Renshaw cells, which excludes their mediation by interneurones responsible for Ia reciprocal inhibition. The study leads to the conclusion that the inhibition of d.s.c.t. cells from group I afferents is, at least in part, collateral to the non‐reciprocal inhibition of lumbar motoneurones.

Neck muscle afferent input to spinocerebellar tract cells of the central cervical nucleus in the cat

SummaryExtracellular and intracellular recordings were made from spinocerebellar tract neurones of the central cervical nucleus (CCN) in C1–C3 segments of the anaesthetized cat. These neurones were identified by antidromic activation from the cerebellar peduncle. Stimulation of the ipsilateral dorsal root elicited extracellular spikes or EPSPs with a monosynaptic latency in almost all CCN neurones in the same segment (segmental input). Late excitatory effects were also observed in about one third of CCN neurones. The monosynaptic EPSP was occasionally followed by an IPSP. The excitatory input from the dorsal root to CCN neurones was extended over several segments for some CCN neurons (extrasegmental input). Monosynaptic excitation was evoked in CCN neurones after stimulation of dorsal neck muscle nerves as well; i.e. splenius (SPL), biventer cervicis and complexus (BCC), rectus capitus dorsalis, and obliquus capitus caudalis. Thresholds for this excitation were near the threshold of the nerve, suggesting that it originated from group I fibres. The component of excitation added after strong stimulation of neck muscle nerves would be attributed to group II fibres. When a CCN neurone received excitatory input from the nerve of one muscle, it was generally not affected by stimulation of other nerves in the same segment. Such muscle specificity of segmental input was the principal pattern of connexion of neck muscle afferents with CCN neurones. In some cases, however, excitatory convergence from SPL and BCC nerves onto single CCN neurones or excitation from the SPL nerve and inhibition from the BCC nerve were also observed. Nearly half of the CCN neurones received input from one muscle nerve of the same segment and not from the afferent of the same muscle of different segments, indicating a segment specificity of input. In the remaining CCN neurones, weaker excitatory effects were induced from afferents of different segments as well. In such extrasegmental effects, inputs to CCN neurones from caudal segments predominated in frequency over those from rostral segments. The origin of extrasegmental input was generally confined to the same muscle. Low threshold muscle afferents from the SPL and BCC were intraaxonally stained with HRP. The collaterals of the stained fibre distributed branchlets and terminals to the CCN, laminae VII, VIII, and motor nuclei. Two fibres responding to local muscle prodding or stretch showed a similar morphology. The findings indicated that muscle spindle afferents from primary endings projected to the CCN.

Inhibition of dorsal spinocerebellar tract cells by interneurones in upper and lower lumbar segments in the cat.

The topographical distribution of interneurones mediating disynaptic inhibition of dorsal spinocerebellar tract (d.s.c.t.) cells from group I muscle afferents in the cat was investigated using both physiological and morphological techniques. Lesions of either the dorsal funiculi or of the lateral and ventral funiculi were made between L4 and L5 segments in two groups of cats. I.p.s.p.s. evoked from group I afferents were seen after both these lesions, showing that the i.p.s.p.s were evoked by interneurones located more caudally as well as by interneurones in the same segments as Clarkes column. Distribution of the caudally located interneurones in the lower lumbar segments was investigated after marking these interneurones with horseradish peroxidase retrogradely transported from Clarkes column. The horseradish peroxidase was injected along L3‐L4 segments of Clarkes column in two cats with transected dorsal funiculi. The marked cells were found in L5, L6, L7 and S1 segments, with a highest density in L6 and L7. They were seen in laminae V, VI and VII. A search was made for interneurones which could be antidromically invaded following stimuli applied in Clarkes column and were monosynaptically excited by group I afferents. Such interneurones were found at locations corresponding to laminae V‐VI of Rexed. The latencies of antidromic and orthodromic responses were within ranges allowing them to mediate disynaptic inhibition of d.s.c.t. cells.

The Neck and Labyrinthine Influences on Cervical Spinocerebellar Tract Neurones of the Central Cervical Nucleus in the Cat

Publisher Summary This chapter investigates the cerebellar projection areas and the input to the spinocerebellar tract (SCT) originating from the central cervical nucleus (CCN) by electrophysiologically in the cat. The CCN-spinocerebellar tract has now been identified as (1) receiving synaptic inputs from both the neck and the labyrinths, and (2) projecting to the vermis of the anterior lobe and to the posterior lobe. Experiments indicate that the input from the neck to CCN-SCT cells is primarily of joint origin probably from the same afferents which initiate tonic neck reflexes, influence extraocular motoneurones, and project to the flocculus. Wilson et al. have shown that the joint afferent impulses are relayed by neurones of Brodal and Pompeianos group x; the latter neurones do not receive input from the labyrinth in contrast with the CCN cells, the majority of which are co-excited by impulses from both the neck and vestibular afferents.

Spinocerebellar tract neurones with long descending axon collaterals

Studies of the axonal trajectory of the spinocerebellar tract neurone have so far been focused mainly on its stem axon, projecting (directly) to the cerebellar cortex and thus characterizing the cell as spinocerebellar. There is, however, increasing evidence indicating the existence of collateral branches terminating outside the cerebellar cortex. Observations of these collaterals have been concerned mostly with supraspinal structures such as the cerebellar nuclei 9, the vestibular nuclei 6, the nucleus Z 4. Little is known regarding the collateral branchings within the spinal cord 1°. Morphologically it has been shown that some of the funicular neurones in the spinal cord send collateral branches to the spinal grey from their longitudinally running axons, or even possess both ascending and descending axonal branches bifurcated in T-shape near the level of their cell bodies3, s. There would be no reason to assume a priori that these do not apply to the spinocerebellar tract cells, and in fact we found a group of spinocerebellar tract cells in the cervical cord which issue collateral branches descending to the lumbar cord, as will be described below. Of interest in this connexion is the recent physiological finding that neurones in the upper cervical cord receiving synaptic inputs from corticospinal and rubrospinal tracts give off both descending and ascending axons, projecting to the forelimb motor nucleus and the lateral reticular nucleus respectively (Illert and Lundberg, personal communication). Experiments were performed on cats anesthetized with pentobarbital sodium (40 mg/kg) and immobilized with gallamine triethiodide. A glass capillary microelectrode (2 M potassium citrate) was inserted into the spinal cord at the seventh cervical through first thoracic segments to record from neurones of the spinocerebellar tracts. These neurones were identified as spinocerebellar by antidromic invasion from the cerebellum. The method of antidromic stimulation in the cerebellum and criteria for identifying the response as antidromic were described previously, i.e. (1) an all-or-none appearance of spikes at a fixed latency and (2) capability to follow repetitive stimuli at high frequenciesL At the lowest thoracic segment the spinal cord was split into right

A physiological study of identification, axonal course and cerebellar projection of spinocerebellar tract cells in the central cervical nucleus of the cat.

SummarySpinocerebellar tract (SCT) neurones in and around the central cervical nucleus (CCN) were physiologically identified by antidromic activation of these cells on stimulation of the cerebellum. Among the Spinocerebellar tract cells thus identified, those ascending the contralateral spinal funiculi were found in the CCN and ventralwards, whereas those ascending the ipsilateral funiculi existed mostly dorsal to the CCN partly overlapping with crossed cells in the nucleus. Mapping sites from which CCN cells were antidromically activated showed that axons of the CCN-SCT cross at the same segment, ascend the ventral funiculus initially, the lateral funiculus at rostral C1 and the lateral border of the medulla to reach the cerebellar peduncle, enter the cerebellum mainly via the restiform body but possibly also via the superior peduncle. Systematic mapping of stimulation within the cerebellum indicated that the CCNSCT projects to the medial part of the anterior lobe and the posterior lobe bilaterally. Projection to lobules I–II was found in almost all CCN-SCT cells examined. Three fourths of CCN-SCT cells projected to the posterior lobe, as revealed by less extensive mapping. Mapping of axonal regions of the same single CCN-SCT cells showed that they project multifocally in the cerebellum, where projection to lobules I–II was common and that to other areas varied with individual cells. Conduction velocites decreased within the cerebellum probably as the result of repeated branching. Mossy fibre responses evoked on stimulation of the C2 dorsal root in cats with the transected dorsal funiculi were shown to be mediated mostly via the CCN-SCT. Mapping the field potential showed that the response was by far the largest in lobules I–II. This suggested that the terminals provided by the CCN-SCT are the densest in these lobules.

Heterogeneous composition of the spinocerebellar tract originating from the cervical enlargement in the cat

The spinocerebellar tract originating from the cervical cord (or RSCT, for rostra1 spinocerebellar tract) has been characterized to date as a system of neurones that receives monoor disynaptic activation from high threshold group I muscle afferents. It has been proposed to be a forelimb equivalent of the hindlimb’s ventral spinocerebellar tract (VSCT) on the basis of similar modes of afferent connection and cerebellar terminationc-8. A more rigourous comparison would equate the RSCT with the Ib-VSCT component from the hindlimb and not the SCB-VSCT component that originates from spinal border cell&s. Most information on the RSCT has been based on axonal recordings in the spinal funiculus. As a result little is known regarding the location and exact synaptic connections of its cell bodies 214. This report gives some preliminary results on these two problems as derived from an electrophysiological study in which RSCT cells were identified antidromically and tested to see if they formed as homogenous a group as hitherto considered. Experiments were performed on adult cats anesthetized with a-chloralose (50 mg/kg) or pentobarbital sodium (35 mg/kg) and immobilized with gallamine triethiodide. Cg to Ti neurones were sought which could be antidromically activated from the cerebellum as revealed by intraor extracellular recordings with micropipette electrodes (2 M potassium citrate). For ipsilateral antidromic stimulation an array of 4 tungsten needle electrodes was inserted into the cerebellum. Electrode tips (2 mm apart) were positioned in the white matter of the anterior lobe (Horsley-Clarke coordinates approximately P 6-10 mm, L l-3 mm, H +l mm). Neurones were identified as ‘spinocerebellar’ if they could be excited from the cerebellum at low stimulus threshold (200 ,uA for 0.2 msec duration pulses) with fixed latency and if they could further follow repetitive shocks up to 3OO/sec. Bipolar silver ball electrodes were placed bilaterally on the surface of the C4 lateral funiculus for ipsilateral and possible contralateral antidromic stimulation of the ascending axons. To examine

Axonal trajectory of single group Ia and Ib fibers in the cat spinal cord

Abstract Intracellular staining with HRP of physiologically identified group Ia and Ib afferent fibers in the adult cat lumbosacral cord revealed that group Ia and Ib fibers take a similar course in the dorsal funiculus, but the collaterals emerging from them show a different topographical distribution and a different mode of branching in the gray matter. Ia collaterals terminate in laminae VI, VII, IX, and sometimes VIII, whereas Ib collaterals terminate only in lamina VI, or both VI and IX. In lamina IX, two large motor-type neurons received terminations of both Ia and Ib fibers at the same time.