Abstracts

Previous studies described that mice in different strains show different seizure susceptibility to systemic administration of the kainic acid (KA). Limbic seizures in mice induced by KA microinjection, however, remain obscure. In the present study, we investigated seizures following microinjection of the KA into the amygdala in mice with different strains. Twelve mice with two strains (C57BL/6 (n=6), FVB/N (n=6)) underwent implantation of electrodes in the left amygdala (LA) and the left sensorimotor cortex (LCx). Stainless cannula was also inserted into the LA for KA injection,. All animals received KA injection into the LA (0.5ɠg) to induce seizures, Electroencephalographic and behavioral observation was made for 48 hours and voltages of the spike were statically analized. Mice then were decapitated and histologic studies including analysis of the neuronal density of the CA3 in the hippocampus were carried out. On electoroencephalograms (EEGs), multiple spike discharges initially appeared in the LA within 10-20 min after KA injection and mouth and facial movement were behaviorally observed in both strains. At 20-60 min after KA injection, the seizure discharge propagated to the LCx. Within 60-90 min after KA injection the amplitude of the multiple spike discharges increased, seizure spread to the LCx , and head nodding , forelimb clonus , rearing and falling and generalized tonic clonic seizures were behaviorally observed. During ictal EEG change, all mice showed only immobilization , lasting 1-2 min and recurring every 10-20 min. In the C57BL/6, at 48 hours after KA injection multiple spike discharges were disappeared. Unlike C57BL/6, multiple spike discharges in the FVB/N were still apparent even at 48 hours after KA injection. Spike amplitude of the LCx in the FVB/N was statistically greater than that in the C57BL/6 at 48 hours after KA injection. Neuronal damage in the CA3 region was significantly more dense in the FVB/N than in the C57BL/6. In the KA-induced amygdalar seizures, it is likely that mice of the FVB/N strain show more seizure susceptibility than those of the C57BL/6. (Supported by Grant[ndash]in-Aid for Encouragement of Young Scientists from the Ministry of Education, Sciences, and Culture of Japan.)