Abstracts

Rationale: Epilepsy is a chronic neurological disorder characterized by spontaneously recurrent seizures and comorbid disorders that include deficits in learning and memory. While current antiepileptic drugs (AEDs) target seizures, they do not treat the comorbidities and may exacerbate these disorders. Recent studies using acquired epilepsy models suggest that seizures may induce learning and memory deficits as well as hyperactive signaling of the phosphoinositide 3-kinase (PI3K) and mechanistic target of rapamycin (mTOR) cascades. In physiological conditions, activation of these pathways is sufficient to promote protein synthesis, dendritic spine remodeling, and learning and memory, yet whether the hyperactivation of PI3K-mTOR underlies behavioral deficits following a seizure remains unclear. We evaluated the role of a single generalized seizure on PI3K and mTOR signaling, dendritic structure, and behavior. In addition, we tested whether inhibition of these cascades would restore the behavioral deficits.Methods: Rats were administered saline (controls) or the chemoconvulsant pentylenetetrazole (PTZ) to induce a generalized seizure. To determine how a seizure affects PI3K and mTOR activation, brain tissue was harvested at 3 time points (1, 3, and 24 hours) and processed for western blotting (WB) for phospho (P) AKT at threonine 308 and P-S6 at serine 240/244. Spine structure was assessed using Golgi staining and tracing. Using a separate cohort of animals, we tested short-term (STM) and long-term (LTM) memory using the Fear Conditioning (FC) assay. Finally, we tested whether wortmannin (Wort) or rapamycin (Rap), PI3K and mTOR inhibitors, respectively, would restore the seizure-induced learning and memory deficits.Results: P-AKT and P-S6 levels were significantly elevated at 1- and 3-hours post seizure relative to controls (p<0.01). At 24-hours post seizure, both P-AKT and P-S6 levels returned to basal levels. Analyses of spine structure reveal that seizures result in a significantly increased length-to-width ratio and a decreased number of mushroom spines as compared to control animals (p<0.05). When tested for STM, there were no significant differences in seizure relative to control rats in the FC task (p>0.05). However, only seizure animals exhibited significant deficits in LTM (p<0.0001). Rap did not restore seizure-induced memory deficits, while Wort partially restored these deficits.Conclusions: Our findings reveal that a single generalized seizure is associated with signaling cascade alterations, changes in spine maturation, and deficits in long-term memory. In addition, our studies show that inhibition of PI3K signaling may restore seizure-induced memory deficits. Studies are underway to further characterize how seizures affect other memory types and the associated molecular signaling and morphological alterations.