Seizure Irradiation during Functional Elimination of the Thalamus by Spreading Depression in the Rat

SUMMARY The effects of thalamic spreading depression on different forms of epileptic activity were studied in 42 unanaesthetized curarized rats. Afterdischarge evoked by cortical or hippocampal stimulation (1 msec, 20/sec, 5–10 sec) applied during functional elimination of thalamus are considerably shorter than those evoked under control conditions. This result is due to an interference with the mechanism of seizure generalization caused both by primary and secondary effects of thalamic spreading depression. Also early stages of epileptic activation caused by intraperitoneal injection of metrazol (100 mg/kg) are blocked by thalamic spreading depression for about 100 sec. A fully developed afterdischarge or metrazol seizure is not stopped by thalamic spreading depression, however, although the EEG patterns in different brain areas may be considerably modified. It is concluded that the thalamus plays an important role in triggering a generalized epileptic seizure, but that it is not indispensable for sustaining it. RÉASUMÉA Les auteurs ont eAtudieA chez 42 rats non anestheAsieAs les effets de la “spreading depression” thalamique sur diffeArents types d'activiteA eApileptique. Les post‐deAcharges provoqueAes par stimulation corticale ou hippocampique sont consideArablement raccourcies par l'eAlimination fonctionnelle du thalamus qui est eAgalement susceptible d'empeCcher pendant environ 100 sec les stades preAcoces de l'activation eApileptique provoqueAe par injection intrapeAritoneAale de cardiazol, alors qu'elle est sans effet sur une crise cardiazolique pleinement deAveloppeAe. Il peut donc eCtre admis que le thalamus joue un roCle important dans le deAclenchement des crises eApileptiques geAneAraliseAes mais qu'il n'est pas indispensable pour le maintien de ces crises.