Abstracts

Rationale: Epilepsy is a group of conditions characterized by the sporadic occurrence of seizures. It is a major public health problem and is estimated to affect 1 in 26 people in their lifetime. Approximately 30% of patients taking antiepileptic drugs (AEDs), however, cannot control their seizures with drugs alone. In addition, adverse side effects such as cognitive impairment are common. This may be because current AEDs act as central nervous system depressants and target neuronal channels to control tissue excitability. Therefore, new drugs based on non-neuronal targets may serve as novel therapeutic strategies with fewer deleterious effects. Astrocytes maintain glutamate and water homeostasis primarily through glutamate transporter-1 (GLT1) and aquaporin-4 (AQP4), respectively. Previous work has demonstrated that alterations in both glutamate and water homeostasis would be expected to have powerful effects on excitability. However, the regulation of GLT1 and AQP4 in epilepsy is not well understood. Methods: In this study, we used intrahippocampal kainic acid (IHKA) injections in CD1 male mice to induce convulsive status epilepticus (SE) that subsided spontaneously. After a latent period of approximately one week, mice experienced chronic recurrent seizures and progressive sclerosis of the hippocampus. We used real-time polymerase chain reaction (RT-PCR), Western blot, and immunohistochemical analysis at 1, 4, 7, and 30 days post SE to determine hippocampal AQP4 and GLT1 expression changes during epileptogenesis. A separate group of mice received intrahippocampal injections of saline as a control. For each condition, n=5 CD1 male mice were used. Results: We found an earlysignificant reduction in AQP4 dorsal hippocampal protein expression 1 day after SE with recovery over time. In the sclerotic hippocampus at 30 days, AQP4 protein expression was significantly upregulated. Increases in AQP4 mRNA were also observed. An initial increase in dorsal hippocampal GLT1 expression was observed as early as one day post SE. This significant increase subsided by 4 days post SE and was then followed by a significant and persistent downregulation of GLT1 protein. Little change in GLT1 mRNA was observed at any time point examined. Conclusions: We found significant changes in AQP4 and GLT1 expression in the intrahippocampal kainic acid model of epilepsy. Our findings suggest that alterations in AQP4 and GLT1 expression and/or localization may contribute to epileptogenesis during the "latent" period prior to onset of spontaneous seizures in this model. Future studies will characterize the mechanisms and functional relevance of AQP4 and GLT1 regulation during epileptogenesis. Funding: This project was supported by NIH RO1s NS082570 and NS081243.