Discharges of nucleus interpositus neurones during locomotion in the cat.

Abstract

SUMMARY1. Extracellular recordings were made from ninety-five cerebellar nuclear neurones in the cat. All were studied during periods of steady walking at 0'5 m/s and most were also studied in the resting animal.2. Most neurones were in nucleus interpositus anterior; forty-four cells were shown by antidromic invasion to project to the mid-brain.3. Most neurones discharged tonically in the absence of overt movements and the mean rate was 42 impulses/s (S.D.+ 23). During locomotion the mean rate was 68 impulses/s (S.D.+ 32).4. In all but seven neurones the discharge during locomotion was frequency modulated but in different neurones the depth of modulation varied from 5 to 161 impulses/s (mean 52 impulses/s; S.D. + 30) and the time of peak discharge relative to the step cycle in the ipsilateral forelimb also varied widely.5. Despite the individual differences the population as a whole was much more active during forelimb swing than during stance, both in numbers of neurones strongly active and in over-all average discharge rate (74 impulses/s as compared with 55).6. Most neurones had tactile receptive fields on the ipsilateral forelimb while others received input from head and neck or from both ipsilateral limbs. The tendency to discharge preferentially during early swing was greatest for the first group, especially the subpopulations with receptive fields around or proximal to the elbow.7. Cells encountered in close sequence during a micro-electrode track had similarly located receptive fields and usually showed similar patterns of discharge during locomotion.8. These findings are discussed in relation to the suggestion by Orlovsky (1972 a, b, c) that nucleus interpositus assists in regulating locomotion by evoking rubrospinal discharges which facilitate the flexor muscle activities produced by the spinal mechanisms reponsible for generating the swing phase of the step cycle.

Discharges of Purkinje cells in the paravermal part of the cerebellar anterior lobe during locomotion in the cat.

“…The Purkinje cells were recorded in the same cats as were used by Armstrong & Edgley (1984) for an investigation of the impulse activity in nucleus interpositus during locomotion.…”

“…The techniques for the animal training, the preparative surgery, the micro-electrode and electromyographic recordings, the receptive field determinations, the data processing and the histological controls were those of Armstrong & Edgley (1984).…”

“…The present recordings were carried out principally to throw light on the sources of input responsible for the rhythmic discharges found among neurones of an intracerebellar nucleus (nucleus interpositus) during locomotion under the same conditions (Armstrong & Edgley, 1984). As a population, cells located in the caudal part of nucleus interpositus anterior and with receptive fields on the ipsilateral forelimb discharged much more vigorously during the swing than the stance phase of the step cycle in the same limb.…”

“…Some were shown electrophysiologically to PURKINJE CELLS AND LOCOMOTION belong to the cl cortical zone or to the c2 zone. The former population can be presumed to have projected to (and therefore monosynaptically inhibited) the population of forelimb-related neurones in nucleus interpositus studied by Armstrong & Edgley (1984) which were encountered deeper in the same micro-electrode tracks.…”

“…There are two major sources of input to interpositus neurones and either or both might be responsible for generating the rhythmic discharges observed by Armstrong & Edgley (1984). Monosynaptic excitation is provided by collaterals from some of the mossy-fibre and climbing-fibre afferents which pass around and through the nucleus en route to terminate in the overlying paravermal part of the cortex (see Chan-Palay, 1977;Bloedel & Courville, 1981 for references and discussion).…”