The aim of this study was to test the hypothesis that nonconvulsive seizures elicited by a low dose of kainic acid may induce acute as well as chronic changes in brain function. Cortical epileptic afterdischarges (ADs) characterized by spike-and-wave rhythm and clonic seizures of facial and forelimb muscles were elicited in adult male rats with chronically implanted electrodes. Four stimulations were given in each of four weekly sessions. In the second session, 26 animals were injected with kainic acid (6 mg/kg i.p.) and 19 rats received no injection. The acute effects of kainic acid were to increase the intensity of movements accompanying stimulation and abruptly prolong ADs. Epileptic ADs were followed by a depression of electrocorticographic activity in both noninjected and kainic acid groups. In addition, when kainate was administered, interictal spike activity was registered mostly in the occipital region. One and two weeks after kainate administration, i.e. in the third and fourth stimulation sessions, there was an increased incidence of transitions from spike-and-wave ADs to another, limbic type of afterdischarge. This functional change persisted although no obvious neuronal death was found in the hippocampi of 12 other rats that received the same dose of kainic acid.

Institute of Physiology Academy of Sciences of the Czech Republic Prague

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