Inhibitory action of Purkinje cells in the posterior vermis on fastigio-prepositus circuit of the cat.

Neuronal connections between the posterior vermis including the fastigial nucleus and the prepositus nucleus were studied with electrophysiological and neuropharmacological methods in the cat. Spontaneous discharges of neurons in the prepositus nucleus were depressed by microstimulation of the contralateral vermis, lobule VI. This depressive effect was blocked by the injection of bicuculline into the caudal part of the fastigial nucleus. These prepositus neurons also showed long-lasting poststimulus facilitation following microstimulation of the contralateral fastigial nucleus. These prepositus neurons were reciprocally connected with neurons in the contralateral fastigial nucleus. These findings suggest that Purkinje cells in lobule VI of the vermis depress propositus neuronal activity through the fastigial nucleus and that the reciprocal connectivity between the prepositus and fastigial nuclei generates a significant background facilitation in the two nuclei.