Abstracts

Rationale: Targeted deletion of the PTEN, tumor suppressor in a subset of neurons (GFAP-Cre; PTEN^loxP/loxP) in mice induces a progressive epilepsy phenotype (starting between 2-4 weeks). Previous studies have shown that treatment with the mTOR inhibitor, rapamycin decreased epilepsy progression in the neuron subset-specific PTEN (NS-Pten) knockout (KO) mice. In these studies we subjectively identified improvements in the background EEG activity in addition to suppression of epileptiform activity in the NS-Pten KO mice following rapamycin treatment. In order to quantify the changes in the background EEG activity we analyzed the EEG dynamics in adult NS-Pten KO and wild type (WT)mice before and after rapamycin treatment using Fast Fourier Transformation (FFT). Methods: Mice were video-EEG monitored for 4h at 8, 12, and 13 weeks of age (Nicolet v32 Amplifier). Rapamycin (rap) or vehicle (veh) was injected daily (10mg/kg; i.p.) starting at 9 weeks of age. 10 sec epochs of the baseline interictal EEG signals were randomly chosen (sampling rate of 250Hz, filtered between 0.5 and 70 Hz) after the first 30min of recording up to the end of the recording session and analyzed using FFT (LabChart 7, AD Instruments) to determine total and relative spectral power of Δ(1-4Hz), θ(4-8Hz), α(8-13Hz), β(13-30Hz) and γ(30-50Hz) bands. Total power was expressed as the percent difference between the averaged data at 8 weeks and 12-13 weeks. Spectral bands (normalized as a percentage of total power) were calculated for averaged data at 8 weeks and 12-13 weeks. Results: Total power between 0.5 to 50Hz increased by 45.1±13.9% (p<0.05, n=6) at 12-13 weeks of age in the veh-treated KO mice compared to 8 weeks of age. In contrast, the total power decreased over this period by 38.5±17.9 % (p<0.05, n=5) in the veh-treated WT group. In rap-treated KO mice total power decreased by 40.3±50.0 % (p<0.05, n=5) over time making it comparable to the veh-treated WT group. Rap treatment did not alter the spectral analysis in the Δ, θ, α, β, and γ bands in the KO or WT mice. However, veh-treated KO mice demonstrated higher power in the upper frequencies (23 to 30Hz) of the β bandwidth (0.8± 0.04 in KO vs. 0.6±0.05 in WT, p<0.05) and γ bandwith (p<0.05) at 8 weeks as compared to veh-treated WT mice, which was no longer detected at 12-13 weeks (p=NS). Conclusions: Our results reveal that rapamycin suppresses the increase in total power in NS-Pten KO mice after 3-4 weeks of treatment to levels comparable to the WT group. No drug effect was observed on the spectral analysis independently of the genotype. These observations could be attributed to an effect of rapamycin on synaptic pruning, while preserving the hierarchy of brain oscillations. Interestingly, at early adult ages KO mice present higher power in faster frequencies that resolve with time. This possibly reflects a delay in brain development in NS-Pten KO compared to wildtype mice. Funding: NIH R01 NS81053; 39943, Vivian L. Smith Foundation Research Grant, CURE Challenge Award, Epilepsy Foundation Predoctoral and Postdoctoral Fellowships, and in part by NIH P30HD 024064