Abstracts

Rationale: Epilepsy comprises a group of conditions characterized by the sporadic occurrence of seizures and unconsciousness. It is a major public health problem and is estimated to affect 2% of the population. Approximately 30% of patients taking antiepileptic drugs (AEDs), however, have poor seizure control and are medically refractory. In addition, since AEDs primarily act as central nervous system depressants, adverse side effects such as cognitive impairment are common. Most current AEDs target neuronal channels to control tissue excitability but since excitotoxic neuronal degeneration and astrogliosis are hallmarks of epilepsy, new drugs based on astrocyte-specific targets of glutamate metabolism are an appealing alternative approach with potentially fewer deleterious effects. Glutamate transporter-1 (GLT1) is an astrocyte-specific membrane protein that is responsible for >90% of glutamate clearance from the extracellular space. The regulation of GLT1 in epilepsy models, however, is not well understood.Methods: In this study, we used intrahippocampal kainic acid (IHKA) injections to induce convulsive status epilepticus (SE) that subsided spontaneously in the adult mouse. After a latent period of approximately one week, mice experienced chronic recurrent seizures and 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 GLT1 expression changes during epileptogenesis. A separate group of mice received intrahippocampal injections of saline as a control. For each condition, n=5 mice were used.Results: We found a significant initial increase in hippocampal GLT1 immunoreactivity as early as one day post status epilepticus (SE) in the adult mouse brain. This significant increase subsided by 4 days post SE and was then followed by a significant and persistent downregulation of GLT1 immunoreactivity. Although local GLT1 expression changes were observed, the overall hippocampal protein and RNA expression of GLT1 did not differ from control mice.Conclusions: We found dramatic and significant changes in GLT1 immunoreactivity in the intrahippocampal kainic acid model of epilepsy. Our findings suggest that alterations in 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 GLT1 regulation during epileptogenesis. This project was supported by NIH RO1s NS082570 and NS081243.