A Study of Epileptiform Hippocampal Unit Activity Induced by Intracerebroventricular Injection of Kainic Acid in Rats

Hippocampal EEG and unit activities were recorded after seizures were initiated with intracerebroventricular injection of kainic acid (KA) in rats. Three kinds of hippocampal unit re- sponses to KA were found: 1. Positive units: These units were characterized by high frequency burst firing temporally coincident with each hippocampal EEG spike. 2. Negative units: These units showed a cessation of firing during each EEG paroxysm. 3. Indifferent units: These units showed no evident chanses coincident with EEG paroxysms. Most positive units were hippocampal complex spike cells which correspond histologically to hippocampal pyramidal cells, and most complex spike cells fired in positive bursts after KA treat- ment. In the early period after KA injection, the positive units were concentrated in CA3 area. It was suggested that the activities of positive units may be considered as the typical epileptiform hippocampal unit activity induced by KA, and the firing features of negative units ma be the result of the influence of hippocampal inhibitory interneurons or the result of excessive cellular depolarization, and that hippocampal pyramidal cells were more sensitive to the epileptogenic ef- fect of KA than hippocampal intemeurons, and some pyramidal cells in CA3, in particular, may serve as "epileptic pacemaker neurons " in KA-induced epileptogenesis.