[Convergence effects evoked in neurons of the thalamic ventrolateral (VL) nucleus by the stimulation of paleo- and neocerebellar nuclear efferents].

The functional characteristics of the cerebellar nuclear outputs (fastigial, F.; interpositus, I.; dentate, D. nuclei) convergence on single neurones of th ventrolateral (VL) thalamic nucleus were studied in chloralosed, curarized and artificially ventilated cats (pCO2 continuously monitored), by means of the usual electrophysiological stimulation and intracellular recording techniques. From the experimental results on 90 VL n. neurones, with the analysis of the evoked cerebellar nuclear outputs unitary responses, it is possible to conclude: a) 69% of the reactive VL n. units are convergence neurones (CN); b) 34% of the CN are reactive to stimulation of all three cerebellar nuclei, showing similar patterns, with predominantly excitatory effects when located in the dorso-medial VL n. region and opposite patterns (excitation and inhibition) when located in the ventro-lateral VL n. region; c) 30% of the CN are reactive to the F.n and I.n. stimulation, often with opposite patterns; d) 36% of the CN are reactive to the D.n.-F.n. and D.n.--I.n. stimulation, usually with similar patterns. From this evidence, the effects evoked by the D.n. stimulation on to VL n. neurones seem to potentiate the F.n. and I.n. actions, whereas teh convergent F.n.-I.n. inputs exert often opposite effects on the same neurone. The dorso-medial and the ventro--lateral VL n. regions also seem to receive different actions from the converging cerebellar nuclear outputs. All the results are functionally discussed in terms of a possible integration between posture and voluntary movements at the level of the thalamic relay nucleus of the cerebello-cortical pathway.