Abstracts

Rationale: Activation of the mammalian target of rapamycin (mTOR) pathway has been implicated in contributing to chronic epileptogenesis in multiple models of epilepsy. In addition, seizures themselves can directly cause acute activation of the mTOR pathway. Our previous work showed a biphasic activation of the mTOR pathway in the kainate model of epilepsy, with an initial acute phase of mTOR activation lasting a few hours stimulated immediately by kainate-induced seizure activity and a second, more chronic phase over a few weeks correlating with the process of epileptogenesis and eventual development of spontaneous seizures. In contrast to the kainate model, pentylenetetazole (PTZ) is an antagonist of the gamma-aminobutyric acid (GABAa) receptor that can cause acute seizures in rodents, but does not usually lead to the development of spontaneous epilepsy. In this study, we tested the hypothesis that PTZ-induced seizures cause acute, but not chronic mTOR pathway activation. Methods: Six-week old SD rats were injected with a single dose of PTZ (75 mg/kg, i.p.). The latency and duration of convulsive seizure activity were observed behaviorally. Rats were then sacrificed at various times intervals (1, 3, 6, and 16 hours, 1, 3 and 7 days, or 3 and 5 weeks) after the onset of seizures. Vehicle-injected rats served as controls. The neocortex and hippocampus were harvested individually at the different time points. Western blot analysis was performed on phospho-S6 (P-S6) and total S6, with the ratio of P-S6 to S6 expression serving as a measure of mTOR pathway activity. In addition, phospho-Akt and total Akt expression was examined as a potential upstream mediator of mTOR activation. Results: PTZ injection induced acute convulsive seizure activity within a few minutes and caused a corresponding activation of the mTOR pathway, as reflected by an increase in the P-S6 to total S6 ratio. P-S6 expression peaked at 3-6 h and returned to baseline by 16 h after seizure onset in both hippocampus and neocortex. In contrast to the kainate model, there was no secondary chronic increase in P-S6 expression observed over days to weeks following PTZ-induced seizures. Similar to P-S6, phospho-Akt protein expression was upregulated in the first few hours after the onset of PTZ-induced seizures. Conclusions: PTZ-induced seizures result in acute immediate activation of the mTOR pathway, without a later, more chronic effect on mTOR activity. The acute activation of the mTOR pathway by seizures may be mediated through upstream activation of Akt. In comparison to the kainate model, the lack of a late phase of mTOR activation might account for the absence of epileptogenesis and the development of epilepsy in the PTZ model. Future studies aimed at identifying mechanistic differences in mTOR pathway activation between the PTZ and kainate models may provide important insights into mechanisms of epileptogenesis. Supported by NIH NS056872.