Effects of stimulation of cerebellar and thalamic nuclei upon spinal alpha motoneurons of the cat.

Abstract

1. Effects of stimulation of cerebellar and thalamic nuclei on the spinal function were tested by recording monosynaptic reflex discharges from ventral roots and recording intracellular potentials from alpha motoneurons in the lumbar segments of the cat.2. The effect elicited by single pulse stimulation of nuclei was fairly the same between the animals under very light anesthesia and good general conditions. However, it was easily variable with a slight change of the animal conditions.3. Single stimulation of the fastigial nucleus (FN) elicited two group facilitations upon the monosynaptic reflex set up by tibial nerve stimulation (extensor), the one at a latency of about 10msec with a relatively short lapse and the other at a latency of 20-30msec with a long-lasting slow time course of 50-100msec. The facilitations appeared on bilateral bodily sides but more marked on the ipsilateral side than the contralateral. Scarce effect was observed with the FN stimulation upon the reflex set up by peroneal nerve stimulation (flexor).4. Single stimulation of the interpositus nucleus (IN) produced the reciprocal effect that was facilitatory upon the ipsilateral flexor reflex at a latency of 10-15msec while inhibitory upon the ipsilateral extensor reflex at a latency of about 15msec. Somewhat similar but undistinguishable effect was elicited upon the contralateral side.5. The effect of stimulating the dentate nucleus (DN) was characterized by the long-lasting slow facilitation upon bilateral peroneal and tibial reflexes. The facilitation appeared usually at a latency of 50-100msec and continued for about 100msec or more. It was often preceded by the other facilitation of a short latency of 10-15msec and of a relatively short duration.6. Single stimulation of the ventral-lateral nucleus of the thalamus (VL) elicited the facilitation upon bilateral peroneal and tibial reflexes at a latency of about 15 msec although far dominant upon the contralateral side. The time course of the facilitation showed an initial steep increase and a following slow decay. The lapse of the decay was always longer in the extensor reflex than the flexor one.7. Effects of repetitive stimulation of a nucleus were, in usual, deducible from the effect of single pulse stimulation of that nucleus as its temporal summation. However, they were rather complicated when compared with the single stimulation.8. The facilitation and inhibition of the monosynaptic reflex by stimulating cerebellar and thalamic nuclei seemed, in almost all cases, to be elicited by PSP mechanism in motoneurons which was produced directly or indirectly with descending impulses through spinal tracts.9. DN stimulation set up the inhibitory effect upon some motoneurons without any remarkable membrane potential change. Analyses of the effect showed, however, that the inhibition may be due to the shunting effect of the motoneuronal membrane by both EPSP's and IPSP's which converged to the motoneuron with a balancing amount and were neutralized mutually at the resting potential level.10. Most of PSP's in motoneurons elicited by the cerebellar and thalamic stimulation, especially the late group PSP's, were consisted of both EPSP's and IPSP's. Facilitation or inhibition of the motoneurons by the stimulation was the net result of the both PSP's.