Abstracts

RATIONALE: We have previously shown that reduced expression of EAAC1 in adult wild-type rats by antisense treatment (knockdown), led to behavioral abnormalities including staring/freezing episodes and electrographic (EEG) seizures. This effect was specific to EAAC1 (as compared to sense EAAC1, GLT-1 and GLAST antisense), and caused a 50% loss of hippocampal GABA levels. Newly synthesized GABA from extracellular glutamate was also significantly impaired by reduction of EAAC1 expression. In contrast, EAAC1 defficient mice, as reported by Peghini et-al, had no seizure activity by observation (no EEG recorded) and no compensatory change in the expression of other glutamate transporters. We hypothesized that due to the deficit of the transporter protein during ontological development, there may be a comensartory mechanism protecting the deficient mice from epilepsy.
METHODS: In the current study we examined the same EAAC1 defficient mice and investigated the effect of EAAC1 abolishment on spontaneous seizure activity and seizure susceptibility using a seizure behavioral scale, EEG recording and pentylenetetrazol (PTZ) test. We used western blot analysis to compare the expression levels of the other glutamate transporters. We have also compared functional glutamate uptake (total and DHK sensitive) between the EAAC1 defficient mice and wild type controls.
RESULTS: The null mice did not show any freezing/staring episodes, nor did they display any other epileptic activity. Furthermore, EEG recording was normal, and the seizure susceptibility as measured by pentylenetetrazol (PTZ) test was not different from controls (wild-type mice of the same background). In a western blot analysis we found no change in the expression levels of the other glutamate transporters. However, measurements of transport activity (done by glutamate uptake assays) revealed a striking increase in the null animals transport activity, as compared to controls.
CONCLUSIONS: We postulate that during development, a compensation process takes place, which leads to an elevation in other transporters glutamate uptake activity, while not affecting their expression levels. The hippocampal GABA levels, as well as the rate of its production in the EAAC1 null mice are under investigation.
The ability to modify glutamate transporter EAAC1 activity may be an important mechanism of preventing/treating some types of epilepsy.
[Supported by: NIH (Jeff Rothstein) and EFA (Jehuda Sepkuty)]