Cerebello-thalamo-cortical system

I Eiectrophysiological study by intracellular recording

Abstract

The neural connections of the cerebello-thalamocortical pathways of the cat were investigated electrophysiologically. Intracellular recording was performed from pyramidal tract neurons (PTNs) in the motor cortex and relay neurons in the ventrolateral nucleus of the thalamus (VL).
Stimulation of the separate cerebellar nuclei, the interpositus nucleus (INP) and the dentate nucleus (DN), evoked EPSPs with latencies of about 3msec in the fast PTNs. With stimulation of the separate nuclei and intracellular mapping of evoked EPSPs in the motor cortex, it was found that there were many PTNs that receive convergent inputs from INP and DN in the whole area of the motor cortex. Since it is known that the cerebello-thalamo cortical pathway to fast PTNs is disynaptic, the next question was where the convergence of the inputs from both cerebellar nuclei occurred, at the level of the motor corrtex or the VL. By combined stimulation of both nuclei at various intensities, spatial facilitation and occlusion of evoked EPSPs were observed in fast PTNs. This result suggests that the convergence occurred at the level of the VL.
In order to demonstrate this convergence of the inputs from both nuclei in the VL, we performed intracellular recordings from VL relay neurons. Large unitary EPSPs were monosynaptically evoked in a single VL relay neuron after stimulating DN as well as INP. It was concluded that the convergence of the inputs from INP and DN occurs at least partly in the thalamo-cortical neurons of the VL.