The effect of diphenylhydantoin, diazepam and clonazepam on the activity of Purkinje cells in the rat cerebellum.

Spike discharges of single cerebellar Purkinje cells were recorded continuously with extracellular microelectrodes in unanesthetized curarized rats. The intravenous injection of diphenylhydantoin in doses between 10 and 100 mg kg-1 did not substantially alter the activity of Purkinje cells within 2--3 h. The two benzodiazepines, diazepam and clonazepam, already in low i.v. doses (0.03--0.1 mg kg-1) consistently and reversibly depressed the firing rate. Our results do not support the previously advanced hypothesis that these drugs reduce epileptiform activities by increasing the output from the cerebellar cortex. They rather point to the possibility that a reduced firing rate of cerebellar Purkinje cells mediates at least in part ataxia and muscular hypotonia observed after the drugs.