Neuronal stress and injury in C57/BL mice after systemic kainic acid administration

Kainate-induced seizures are widely studied as a model of human temporal lobe epilepsy due to behavioral and pathological similarities. While kainate-induced neuronal injury is well characterized in rats, relatively little data is available on the use of kainate and its consequences in mice. The growing availability of genetically altered mice has focused attention on the need for well characterized mouse seizure models in which the effects of specific genetic manipulations can be examined. We therefore examined the kainate dose-response relationship and the time-course of specific histopathological changes in C57/BL mice, a commonly used founder strain for transgenic technology. Seizures were induced in male C57/BL mice (kainate 10-40 mg/kg i.p.) and animals were sacrificed at various time-points after injection. Seizures were graded using a behavioral scale developed in our laboratory. Neuronal injury was assayed by examining DNA fragmentation using in situ nick translation histochemistry. In parallel experiments, we examined the expression an inducible member of the heat shock protein family, HSP-72, another putative marker of neuronal injury, using a monoclonal antibody. Seizure severity paralleled kainate dosage. At higher doses DNA fragmentation is seen mainly in hippocampus in area CA3, and variably in CA1, thalamus and amygdala within 24 h, is maximal within 72 h, and is largely gone by 7 days after administration of kainate. HSP-72 expression is also highly selective, occurring in limbic structures, and it evolves over a characteristic time-course. HSP-72 is expressed mainly in structures that also manifest DNA fragmentation. Using double-labeling techniques, however, we find essentially no overlap between neurons expressing HSP-72 and DNA fragmentation. These findings indicate that DNA fragmentation and HSP-72 expression are complementary markers of seizure-induced stress and injury, and support the notion that HSP-72 expression is neuroprotective following kainate-induced seizures.