Abstracts

To identify genes whose expression is altered due to recurrent spontaneous seizures, cDNA expression patterns were analyzed in the dentate gyri of the kainic acid (KA) rat model of chronic epilepsy using a combination of high density microarrays and screening in situ hybridizations. Experiments were carried out on 16 wistar male rats after intrahippocampal KA injection. To exclude the effect of KA injection and associated tissue changes, which would confound results, RNA profiles were assayed in two groups of animals: experimental group consisted of 8 rats that had spontaneous seizures for at least 11 months (SZ) and the control group of 8 rats that had similar treatment but did not develop seizure activity (non-SZ). The comparisons were performed between the area of dentate gyri adjacent to the KA lesion and control symmetrical contralateral side. The Rat Microarray (20,000 genes; Agilent Technologies) and the CodeLink Rat Whole Genome array (34,000 genes; GE Healthcare) were used to identify the expression changes. cRNA synthesis, hybridization and scanning were performed according to manufacturer[apos]s protocols. After the local background correction, lowess normalizations were carried out in all distinct pair wise comparisons and ratios were generated. The genes exceeding 1.4-fold change and with P[lt]0.05 were selected as regulated. Gene expression changes were confirmed in a subset of genes using in situ hybridizations with coronal brain sections from at least 3 animals of each phenotype. We detected a number of genes differentially regulated in dentate gyri characterized by chronic seizure activity and confirmed our findings using in situ hybridization. 22% of identified genes were previously implicated in seizure- or epileptogenesis (http://pubmatrix.grc.nia.nih.gov/). To understand the biological significance of the overall changes in gene expression, identified SZ-specific genes were categorized using EASE (http://apps1.niaid.nih.gov/). Only the genes of immune response showed significant enrichment in SZ-rats based on their overall representation on the array (EASE score [lt]0.001). There was no significant overrepresentation of genes related to NMDA, GABA receptors or genes related to different ion channels. To better understand the relevance of our current findings with respect to the human disease selected genes are being analyzed in human biopsy specimens from patients with temporal lobe epilepsy. Significant changes related to seizure genesis at the level of gene expression are not necessarily related to the electrophysiological changes at the neuronal level. This contradicts the existing data indicating the importance of neuron discharges in seizure initiation and requires further studies at the cellular and protein levels. (Supported by NIH NS-33310.)