Differential expression of immediate early genes in the hippocampus in the kindling model of epilepsy

Kindling is a phenomenon in which brief afterdischarges (ADs) evoked by periodic electrical stimulation of the brain eventually result in generalized clonic motor seizures. Once present, the enhanced sensitivity to electrical stimulation is lifelong. The mechanism by which brief ADs produce this long-lasting effect may involve a change in gene expression. To begin to investigate changes in gene expression that occur during kindling, we used in situ hybridization histochemistry to examine the time course of expression of mRNAs of the immediate early genes (IEGs) c-fos, c-jun, NGFI-A, and c-myc within the dorsal hippocampus of rats following a kindling AD. Three principal findings resulted from this study. First, the expression of all mRNAs except c-myc was significantly increased (P < 0.05) within discrete neuronal populations. Second, the time course of expression of the IEGs differed markedly within the same neuronal population. Third, for a given IEG, the time course and anatomic pattern of expression were strikingly different neong different neuronal populations of the hippocampus. The prolonged and distinctly different patterns of IEG expression suggest that target genes are differentially regulated in these neuronal populations for prolonged periods following a kindling AD.