Abstracts

Rationale: Seizure disorders are frequent sequelae of traumatic brain injury. ATP sensitive postassium (mitoKATP) channels couple intracellular metabolic state to electrical activity which is important neuronal excitability and seizure propagation. In many brain regions, mitoKATP channels are expressed pre- and post-synaptically. In addition, picrotoxin induces increases in mRNA expression of GABA transporter proteins. We have also found diazoxide to be protective against CA1 depolarization injury. Therefore, we evaluated if seizure threshold would be lower in a model of in vivo trauma, Controlled Cortical Impact in rats. We also investigated whether diazoxide, a mitoKATP channel opener in clinical use would protect against the induction of epileptiform activity after CCI in rats. Methods: Using rat hippocampal slices harvested from rats that had been subjected to controlled cortical impact (CCI), we monitored the CA1 orthodromic population spike (PS) amplitude during exposure to picrotoxin (100uM) with and without diazoxide (100 uM) treatment. To induce epileptiform activity, slices were exposed to 100 uM picrotoxin for up to 10 min. Treatment with diazoxide was begun 30 minutes prior to picrotoxin exposure and continued for the first 15 min. of after picrotoxin. In another evaluation of post-traumatic seizure threshold, the EC50's for picrotoxin-induced epileptiform activity in slices from CCI and sham rats were compared using a fixed time exposure of 5 min. Results: Diazoxide provided robust protection against the induction of epileptiform activity by picrotoxin in CA1 neurons in hippocampal slices from rats subjected CCI earlier. Slices harvested from rats 24 hours after CCI and then exposed to picrotoxin demonstrated rapid initiation of epileptiform activity in a mean 3.2 ± 0.4 min. Treatment with diazoxide (100 uM) provided significant delay against the induction of epileptiform activity which occurred in a mean 6.8 ± 0.5 min. In hippocampal slices harvested from sham rats (undergoing anesthesia but not CCI), picrotoxin produced epileptiform activity in a mean 7.1 ± 0.4 min. The picrotoxin EC50 for induction of epileptiform activity in slices harvested from sham rats was 65 uM, while that seen in CCI rats marked decreased at 25 uM. Conclusions: These studies demonstrate that when rats are subjected to CCI, CA1 neurons in hippocampal slice 24 hours post-CCI demonstrate a significantly lower threshold for induction of epileptiform activity. These findings also show that treatment with diazoxide provides significant protection against the induction of epileptiform activity following CCI. In addition, these data suggest that the use of agents which modulate the mitoKATP channel may provide a useful strategy against development post-traumatic epileptiform activity. Funding supported by: VA Research Service