Abstracts

Rationale: Recent studies have shown increased mTOR signaling in rodent models of acquired temporal lobe epilepsy (TLE). In these models the development of epilepsy occurs following a prolonged episode of status epilepticus (SE). SE is associated with significant long term morbidity, including the development of spontaneous seizures and cognitive deficits. Given that the mTOR signaling cascade modulates dendritic arborization, spine morphology, and surface expression of ion channels, we evaluated whether excessive mTOR signaling triggered by pilocarpine-induced SE, contributes to alterations in dendritic ion channels and proteins following SE. Methods: Male Sprague Dawley rats at postnatal day ~35 were treated with pilocarpine (Pilo) to induce 1 hr of SE. Vehicle animals (control, CTL) were processed in parallel. After 2 weeks, rapamycin (Rap; 6mg/kg) or vehicle, was administered by intraperitoneal injection every other day for 1 week to suppress mTOR activation in sham (Rap alone) and pilocarpine treated rats (Pilo Rap, or Pilo Veh). We used western blotting (WB, n = 5-8 / group) and immunohistochemistry (IHC, n = 3-4 / group) to evaluate hippocampal protein levels and distribution of S6, 4E-PB1, MAP2, Kv4.2, HCN1 and SK2 channels 3 weeks after SE. Results: We confirmed SE-induced hyperactivation of mTOR signaling based on increased phosphorylation of the mTOR downstream targets, S6 and 4E-PB1 (p < 0.05). WB showed a significant reduction in the protein levels of MAP2, Kv4.2, HCN1 and SK2 in Pilo compared to CTL hippocampi (p < 0.5). IHC showed a loss of MAP2-stained dendrites, and reduced signal of MAP2, Kv4.2, HCN1 and SK2 within the CA1 dendritic fields of Pilo compared to CTL hippocampi (p < 0.05). Rapamycin treatment reversed these changes. Conclusions: Our findings suggest that SE-induced hyperactivation of the mTOR pathway contributes to altered dendritic ion channel homeostasis following SE and suggests a therapeutic role for mTOR inhibition following SE. Supported by NIH, R01 NS, 39943; 49427 (AEA); T32 NS, 43124 (ALB); F32 NS 56664 (JNL).