Abstracts

RATIONALE: The expression of behavioral limbic seizures is age-dependent in humans and animals. The expression of limbic motor seizures following kainic acid administration in rats starts at approximately postnatal age (P)19. In this study we investigated whether the expression of Fos in limbic regions is concomitant with the behavioral expression of limbic seizures. METHODS: Immunohistochemistry for c-Fos protein was examined 1h, 2h, 4h, and 24h after kainic acid-induced seizures (KAIS) or saline administration (controls) in immature rats at P7, P13, and P20. Qualitative and quantitative measurements were used to analyze the expression of Fos-like immunoreactive (FLI) neurons in several brain regions, including neocortex, hippocampus, amygdala, thalamus, hypothalamus, and brainstem. RESULTS: Experimental rats at P20 showed abundant numbers of FLI neurons in the hippocampus and amygdala 1h, 2h, and 4h following KAIS. In contrast, rats at P7 and P13 showed few or no FLI neurons in most amygdaloid nuclei 1h, 2h, and 4h following KAIS. Similarly, few or no FLI neurons were observed in the hippocampus 1h after KAIS in P7 and P13 rats. However, 2h and 4h after the beginning of seizures abundant numbers of FLI neurons were seen in the CA3 field of the hippocampus in P7 rats and in the dentate gyrus, CA1 and CA3 fields of the hippocampus in P13 rats. Rats from all age groups showed abundant expression of Fos in selected nuclei in the thalamus, hypothalamus, and brainstem after KAIS. Few or no FLI neurons were observed in most brain regions in control rats and in experimental rats after 24h of KAIS. CONCLUSIONS: Our results demonstrated that the induction of Fos in most amygdaloid nuclei and the full expression of behavioral limbic seizures following KA administration is rats occur at the same developmental age. The delayed induction of Fos in the CA3 suggests that the activation of the CA3 was not an initial event that triggered motor seizures in the youngest rats.