Abstracts

Rationale: While numerous studies have focused on investigating epilepsy-associated memory deficits, the mechanisms by which a single, generalized seizure perturbs memory remain unclear, a question of clinical relevance. Previous studies have reported that a self-limited seizure is sufficient to impair short and long-term memory in rats. Our lab and others have demonstrated hyperactivation of the phosphoinositide 3-kinase/Akt (protein kinase B)/mechanistic target of rapamycin (PI3K/Akt/mTOR) pathway following a single, generalized seizure. The PI3K/Akt/mTOR cascade is a critical pathway necessary for protein synthesis, dendritic spine remodeling, and memory. Yet, how the seizure-induced hyperactive PI3K/Akt/mTOR signaling underlies the memory deficits is not well understood.For the current studies, we evaluated video-electroencephalographic (vEEG) recordings to: 1) assess neuronal network activity by spectral analysis of EEG frequencies during periods when animals were trained and tested for learning and memory; and 2) to determine whether blocking dysregulated PI3K/Akt/mTOR hyperactivation would reverse the seizure-induced EEG spectral abnormalities. Methods: EEG electrodes were implanted in rats. On the day of seizure induction, the rats were recorded for a 1-hour baseline, and received saline (controls) or pentylenetetrazole (PTZ) to induce a generalized seizure. EEG recordings performed for 25 hours, continuously. EEG spectral analysis was performed at baseline and at time points previously assessed for learning and memory (1, 3, and 24 hours). We assessed total spectral power and the component frequency bands alpha, beta, theta, gamma, and delta. To evaluate how seizure-induced hyperactive PI3K/Akt/mTOR signaling affects EEG spectra, rats were treated with the PI3K inhibitor wortmannin (Wort) or vehicle (Veh) and subsequent spectral analyses were performed. Using western blotting, we verified PI3K/Akt/mTOR pathway inhibition using antibodies against phosphorylated (P)-Akt and P-S6 proteins as readouts. Results: In the PTZ-induced animals, there was a significant increase P-Akt and P-S6 levels (n=3-6 rats/group, p< 0.05). Furthermore, there was a significant increase in the total spectral EEG power at 1 and 3 hours, time points we previously demonstrated short-term memory impairments as compared to controls (p < 0.001).Of the component frequencies, there was seizure-induced increase in theta, delta and alpha frequency band with a concurrent decrease in gamma and beta at 1 and 3 hours compared to control rats (p < 0.001). At 24 hours post seizure, there was no significant difference between the PTZ-induced and control rats. Wort treatment blocked the seizure-induced elevation in P-Akt and P-S6 levels and attenuated the seizure-induced increase in total spectral power at 1 and 3 hours when compared to PTZ + Veh rats (p < 0.05). Moreover, Wort reduced the seizure-induced increase in theta, delta and alpha bands and attenuated the reduction in the gamma band at 1 and 3 hours compared to PTZ + Veh rats (p < 0.05). Conclusions: Our findings reveal that a single generalized seizure is associated with perturbed EEG spectral power at time points previously evaluated for short-term memory deficits. Furthermore, treatment with Wort was able to partially rescue the seizure-induced changes. These findings support transient alterations in neuronal networks following a single generalized seizure that was, in part, due to aberrant PI3K/Akt/mTOR signaling. Funding: The studies detailed in this work were supported by the National Institutes of Health/National Institute for Neurological Disorders and Stroke (NIH/NINDS) R01 NS081053 (AEA) as well as by a NIH/NINDS pre-doctoral fellowship F31 NS080566 (ANC).