Abstracts

RATIONALE: During epileptogenesis, selected cortical circuits undergo a complicated functional reorganization. Numerous contributors to this complex process have been identified, however the relationships between known mediators remain unclear. Furthermore, additional critical mediators of the epileptogenic process likely remain unrecognized. Thus, we are using a combination of techniques to investigate the genetic programs induced during epileptogenesis.
METHODS: We have used two experimental models of epileptogenesis and one acute seizure model to identify essential genetic programs specifically activated during epileptogenesis. DNA microarrays were employed to simultaneously monitor changes in gene expression of thousands of genes in both the dentate gyrus (DG) and CA3 of the mouse hippocampal formation during epileptogenesis. Epileptogenesis was induced with pilocarpine (PILO;300-335 mg/kg) or repetitive injections of kainic acid (KA;20 mg/kg). Seizures were generated in another group of mice with pentylenetetrazol (50 mg/kg). DG and CA3 were each microdissected from hippocampal slices at 1-30 days following treatment. mRNA from each group (n=8 mice) was isolated and reverse transcribed. Amplified RNA was synthesized with T7 RNA polymerase. Fluorescence-tagged probes were prepared (Incyte Gemonics) from all samples for hybridization to microarrays.
RESULTS: We demonstrate distinct, but partially overlapping spatial and temporal patterns of gene expression induced during PILO- or KA-mediated epileptogenesis. The dominant effect of PILO was an increase in gene expression in both regions, whereas a greater number of genes had decreased expression in the KA model. In both models, a greater number of genes has altered expression in the CA3 when compared to the DG. A combination of in situ hybridization and immunohistochemistry are being used to investigate the role of specific gene products in the epileptogenic process throughout the hippocampus. Finally, knockout mice are being used to assess the role of individual genetic targets identified from microarray experiments in the epileptogenic process.
CONCLUSIONS: These results indicate that epileptogenesis produces common patterns of altered gene expression in the hippocampus in multiple experimental model systems. Despite this overlap in both gene activation and inactivation, significant model- and region-specific changes in gene expression also occur in these model systems.
Support: The Epilepsy Foundation (JD), Charles E. Culpeper Foundation (JD), and the NIH.