Abstracts

Rationale: Glutamine synthetase (GS) has been found to be deficient in the hippocampus of patients with MTLE. Recreating a state of GS deficiency by infusing methionine sulfoximine (MSO), a competitive inhibitor of GS, into the entorhinal cortex-hippocampus has been shown to result in spontanenous, recurrent seizures in rats. In this project we study two periods of MSO exposure in the rat brain, namely 72 hrs and 28 days, and analyze the effects on seizure outcome and long-term EEG perturbations. The main question we are asking is if epileptogenesis can be stopped or delayed, and if there are EEG measurements that are markers of this epileptogenic process. Methods: Under Isoflurane anesthesia, a drug delivery cannula was introduced into the right entorhinal cortex and connected to a subcutaneously implanted Alzet osmotic minipump filled with MSO. Two depth electrodes and two screw electrodes were introduced in the dentate gyrus and cerebral hemispheres bilaterally to record EEG activity. A depth electrode and a screw electrode were introduced in the cerebellum to serve as reference and ground respectively. After 72 hours of continuous video-EEG recordings, the pump was removed from a group of the animals via a minimally invasive procedure under anesthesia. The other subset of animals underwent a sham procedure involving a similar incision with comparable anesthesia exposure, while leaving the pump intact. The rats were monitored via video-EEG continuously for a goal of 90 days or until when the implantation fell. Seizures were first identified by visual inspection of the EEG record using Ceegraph Vision Analysis and EEG was subsequently analyzed to quantify changes using Teager energy and spectral band power measurements. EEG was analyzed in three periods: 1) the first 72 hours, 2) day-3 to day-28, and 3) >28. Results: All of the chronically infused rats had seizures. The majority of them continued to have seizures after the 28-day period of infusion. The rats infused with MSO for 72 hours had seizures during infusion, and in a subset seizures were still observed following a latent period but were significantly less frequent. Seizure frequency was not significantly different during the first 72 hours between the 72-hr infusion and 28-day infusion groups, t(18)=0.31, p=0.62. There was a significance difference in the period from day-3 to day-28, t(18)=-7.67, p<0.001. There was a trend toward significance between the groups after day 28, t(18)=-1.50, p=0.07. Teager energy and spectral band measurements pending. Conclusions: One of the key questions is if epileptogenesis can be stopped. Our data suggests that epileptogenesis is an ongoing process that can at least be slowed. Rats who had an acute MSO infusion underwent a long latent period, and though they developed seizures they were less frequent. We will next correlate seizure outcome with Teager energy and spectral band analysis to identify measurements that might be markers of an ongoing epileptogenic process. A better understanding of this epileptogenic process will be critical for patient management and the creation of better targeted pharmacotherapy.