Abstracts

Aquired epilepsy is a condition associated with the development of persistant seizures in previously normal brain tissue, epileptogenesis. Long term plasticity changes have been observed in association with epileptogenesis and it has been suggested that long term gene changes play a role in the development of the epileptic condition (The Neuroscientist 1999;5:886). This study evaluates whether long term changes in gene expression occurred for up to a year after the induction of epilepsy in the pilocarpine model using the powerful technique of DNA microarray analysis to characterize the expression of large numbers of genes.
Epilepsy was induced in rats using the pilocarpine model (Brain Res. 2001;903:1). Animals were monitored to confirm the induction of the epileptic condition. Animals with epilepsy for more than one year and the appropriate controls were sacrificed and hippocampal tissue was rapidly isolated and processed for RNA extraction and characterization (J. Neurosci. 2003;23:2218). Labeled cRNA samples were analyzed on Affymetrix Rat Genome array Set A which represents nearly 7,000 named genes and approximately 1,000 EST sequences. Sample fragmentation, hybridization, and array scanning were performed using standard conditions. The microarray data was analyzed using MAS 5 (Affymetrix) and the S-score algorithm developed in our laboratory (J. Mol. Biol. 2002;317:225).
Microarray studies were performed on at least 4 individual animals from control (C), pilocarpine treated (P) without ongoing epilepsy, or epileptic (E) animal groups. S-score analysis followed by statistical filtering using a permutation method and k-means clustering identified three groups of genes: altered uniquely in E animals, altered in common between E and P groups, and only altered in P animals. Strikingly, groups of genes recently identified by our array studies at 2 weeks post-pilocarpine (J. Neurosci. 2003;23:2218) were also seen in these animals at one year post pilocarpine. A substantial group of calcium signaling genes were uniquely down-regulated in the E animals, perhaps reflecting compensation to long-term alterations in calcium levels with epilepsy. Several genes up-regulated in the P group may play a role in preventing development of epilepsy in those animals.
The results of this study demonstrate that changes in gene expression were observed for as long as one year after the induction of epileptogenesis. Using the advancement of DNA microarray technologies, it was possible to evaluate the hypothesis that long term gene expression contributes to the plasticity changes associated with epilepsy. The results demonstrate expression patterns associated with epilepsy, but also patterns that may protect against epileptogenesis.
[Supported by: Grant R01AA13678 to MFM and Grants R01NS23350 and P50NS25630 to RJD.]