The activity of cerebellar neurones during epileptiform activity induced by penicillin in the cerebral cortex of the rat.

In urethane anaesthetized rats an epileptiform focus was made in one cerebral cortex with penicillin (25 U). The relationship between epileptiform spikes in the cerebral cortex and the activity of cerebellar cortical and nuclear neurones have been investigated by means of extracellular recording techniques and computation of peri-event histograms and 'CUSUMs' (cumulative sums of differences from the mean). In the cerebellar cortex two distinct patterns of evoked activity were recorded: (a) In units showing little or no spontaneous activity, a brief evoked discharge followed the epileptiform spike. (b) In units showing steady spontaneous activity, a period of evoked inhibition followed the epileptiform spike. These included Purkinje cells and probably inhibitory interneurones. In the intracerebellar nuclei, cells with marked spontaneous activity showed a prolonged period of increased discharge following the epileptiform spike. It is concluded that the output of the intracerebellar nuclei is increased by epileptiform activity in the cerebral cortex. The significance of these results is discussed.