Abstracts

Rationale: Current seizure medications may suppress seizures symptomatically, but few drugs have been developed that have true anti-epileptogenic actions in preventing epilepsy. We have recently shown that rapamycin prevents epilepsy in a mouse model of Tuberous Sclerosis Complex by inhibiting activation of the mammalian target of rapamycin (mTOR) pathway. In this study, we have investigated whether the mTOR pathway is activated following kainate-induced seizures in rats and whether rapamycin can prevent mechanisms of chronic epileptogenesis in this model. Methods: Six week old male Sprague-Dawley rats were pre-treated with vehicle or rapamycin (6 mg/kg/d, i.p.) for 3 days. On the fourth day, both groups received kainate (12 mg/kg, i.p.) to induce stage 4-5 seizures. Phospho-S6 (P-S6) expression was assayed by Western blotting at different time intervals after kainate to determine whether the mTOR pathway is activated following kainate seizures and whether rapamycin can prevent this mTOR activation. Histological staining with Fluoro-Jade B and Nissl were conducted to monitor neuronal cell death in hippocampus 8 days after kainate seizures. Some rats were injected with BrdU (50 mg/kg/d, i.p.) from day 3 to day 7 after kainate administration and perfused on the day 8 for immunohistochemical staining with BrdU-specific antibody to detect neurogenesis. Another set of rats were perfused with sulfide solution 4 weeks after kainate injection to detect mossy fiber sprouting. To monitor spontaneous seizures, rats were implanted with hippocampal depth and neocortical electrodes and monitored for seizures by video-EEG for several weeks after kainate. Results: Kainate administration resulted in activation of the mTOR pathway, as evident by an increase in P-S6 expression. The rise in P-S6 started about 1 h after seizure onset, peaked at 3-6 h and returned to baseline by 24-48 h in both hippocampus and cortex. A second peak of P-S6 increase was observed in hippocampus only, which started at 3 days and was maximal 5-10 days after kainate injection. Rapamycin administered for 3 days prior to kainate almost completely blocked kainate seizure-induced activation of mTOR pathway both acutely and chronically. In addition, rapamycin dramatically reduced kainate-induced neuronal cell death, neurogenesis and mossy fiber sprouting. Preliminary video-EEG studies over a couple weeks suggest that rapamycin may also reduce the development of spontaneous seizures, although longer term monitoring of epilepsy is still in progress. Conclusions: mTOR pathway activation may mediate mechanisms of epileptogenesis in the kainate rat epilepsy model. Rapamycin has potential anti-epileptogenic effects in this model.