Purkinje cell responses to a cerebral penicillin-induced epileptogenic focus in the cat

A penicillin focus was induced in the postcruciate region of the cerebral cortex of the cat. Analyzing the Purkinje cell unit responses to consecutive interictal paroxysms, 60% of the cells studied (total number, 148) were found to respond with activation and 25%, with deactivation; the others were not uniform in their responses. These different response patterns were attributed to the high patchy topographic relation between the cerebral cortex and the cerebellar system as well as to the two basic patterns of neural activity, which are generated in the epileptic focus (activation), and its periphery (inhibition). The climbing fiber response to the interictal paroxysms was observed in only 41% of the Purkinje cells of the tuber vermis. This was interpreted as an interference of the epileptic interictal propagation at the inferior olivary complex level. An increase in the simple action potential discharge frequency was found during the ictal phase in intermedial regions of the cerebellar cortex in contrast with the more lateral regions, which showed a decrease; this pattern was inverted during the postictal depression phase. A tentative explanation is made relative to the different functions of the intermedial and lateral cerebellum. During ictal and postictal depression phases, no significant changes were found in the climbing fiber activity.