Increased susceptibility to hippocampal and amygdala kindling following intrahippocampal kainic acid

Abstract

The effects of unilateral intrahippocampal injection of kainic acid, a potent neuroexcitant and neurotoxin, on subsequent susceptibility to kindling of the contralateral hippocampus or contralateral amygdala were investigated in albino rats. At the chosen doses (0.20 to 1.25 μg dissolved in physiologic saline), the kainic acid-induced lesion was confined to the injected hippocampus and in two cases the ipsilateral entorhinal cortex; never were there contralateral lesions. Approximately 2 to 6 weeks post-injection, each animal received daily afterdischarge-producing electrical stimulations until stage 5 kindled limbic seizures occurred. Kindling in pretreated animals was significantly accelerated compared with controls; the hippocampal kindling rate decreased from 13.2 stimulations to 3.7, the amygdala kindling rate from 7.8 stimulations to 3.0. Many treated animals had first-stimulation stage 5 seizures, compared with none for controls. Importantly, this facilitation of kindling was not reversed by suppression of the acute, induced seizures with the anticonvulsants, diazepam and phenobarbital, which have repeatedly been demonstrated to effectively suppress limbic kindling. Such results, considered together with findings from the literature, suggest that partial kindling does not occur during kainic acid-induced seizures, and that the observed susceptibility to kindling and other epileptogenic agents subsequent to kainic acid treatment may in fact be related to neurophysiologic and neurochemical consequences of kainic acid-induced lesions.