GABA, THIP and baclofen inhibition of Purkinje cells and cerebellar nuclei neurons.

The sensitivity of Purkinje cells (PCs) and neurons of the cerebellar nuclei (NCNs) to iontophoretic application of gamma-aminobutyric acid (GABA), 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP) and baclofen, i.e., GABAA and GABAB agonists respectively, have been studied in anesthetized rats. All the agonists produced dose-dependent firing rate depression of the PCs but with different potencies. The inhibitory actions of both GABA and THIP were specifically antagonized by bicuculline (Bic) and the baclofen-induced responses by 2-hydroxysaclofen. GABA and THIP also depressed the spontaneous activity of NCNs while baclofen was ineffective. The present results therefore suggest that GABAA receptors are involved in the GABA-induced inhibition in the cerebellar cortex and in the cerebellar nuclei and GABAB receptors are involved only in the cerebellar cortex.