EFFECTS OF A SUBCONVULSANT DOSE OF KAINIC ACID ON AFTERDISCHARGES ELICITED BY CORTICAL STIMULATION IN RATS

The aim of this study was to test the hypothesis that nonconvulsive se izures elicited by a low dose of kainic acid may induce acute as well as chronic changes in brain function. Cortical epileptic afterdischarg es (ADs) characterised by spike-and-wave rhythm and clonic seizures of facial and forelimb muscles were elicited in adult male rats with chr onically 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. Th e acute effects of kainic acid were to increase the intensity of movem ents accompanying stimulation and abruptly prolong ADs. Epileptic ADs were followed by a depression of electrocorticographic activity in bot h noninjected and kainic acid groups. In addition, when kainate was ad ministered, interictal spike activity was registered mostly in the occ ipital region. One and two weeks after kainate administration, i.e. in the third and fourth stimulation sessions, there was an increased inc idence of transitions from spike-and-wave ADs to another, limbic type of afterdischarge. This functional change persisted although no obviou s neuronal death was found in the hippocampi of 12 other rats that rec eived the same dose of kainic acid, (C) 1997 Elsevier Science B.V.