Blockade of a putative GABA-mediated neurotransmission in the cerebellum by benzodiazepine receptor inverse agonists.

An exponential relationship was observed between the firing rate of cerebellar Purkinje cells in urethane-anaesthetized rats and the duration of inhibition evoked in these cells by electrical stimulation of the nearby cortical surface. Benzodiazepines, administered i.v., decreased cell firing and increased the duration of the inhibitory response but did not alter the relationship between the two parameters. These effects of one benzodiazepine, RU 32007, were reversed by the benzodiazepine antagonist Ro15-1788 which had little effect alone. The benzodiazepine inverse agonists methyl- or ethyl-beta-carboline-3-carboxylate increased cell firing with the expected reductions in duration of inhibitory response in some cases. However, in 50% of recordings the inhibitory response disappeared, independent of the firing rate. All the effects of the beta-carboline esters were reversed by Ro15-1788 or the benzodiazepine, RU 32007. This action of the benzodiazepine receptor inverse agonists represents an in vivo blockade of an endogenous synaptic inhibition which is thought to be mediated by release of GABA.