Abstracts

RATIONALE: The process of epileptogenesis involves a reorganization of neuronal function in cortical circuitry. Numerous studies have identified changes in morphological and physiological neuronal properties during epileptogenesis. However, a comprehensive understanding of the molecular basis of epileptogenesis is lacking. Furthermore, important effects on numerous pathways are likely to remain unrecognized. We are using DNA microarrays to simultaneously monitor temporal changes in gene expression of thousands of genes during epileptogenesis. METHODS: An single injection of pilocarpine (335 mg/kg, i.p.) to CF-1 mice induced an acute status epilepticus (SE). The dentate granule cell layer was microdissected from hippocampal slices taken at 1, 3, and 30 days following the induction of SE. mRNA was isolated from each group (n=8 mice), reverse transcribed, and amplified RNA was synthesized with T7 RNA polymerase. Fluorescence-tagged probes were prepared by Genome Systems from both control and SE-experienced tissue for competitive hybridization to DNA microarrays. RESULTS: A total of 167 genes had changes in expression ratios above the threshold detection limit (2 fold change in expression) for at least one timepoint following induction of SE. The expression ratios of altered genes were subjected to cluster analysis with a self-organizing map algorithm. Different temporal patterns of expression following SE were observed in five distinct gene clusters. At 1 and 3 days post SE, 65 genes had elevated expression and 53 genes had decreased expression. A third cluster of 12 genes showed no change in expression at 1 or 3 days, but elevated expression at 30 days. Finally, at 3 days the expression of 28 genes was selectively elevated and 9 genes depressed. CONCLUSIONS: DNA microarray sensitivity is sufficient to detect mRNAs with a 1:100,000 abundance above background and changes of 70% in abundance between samples. Distinct temporal patterns of gene expression following SE may lead to identification of novel targets for intervention strategies throughout the epileptogenic process. Supported by the Epilepsy Foundation (JD), the Charles E. Culpeper Foundation (JD), and the NIH.