Attenuation of initial pilocarpine-induced electrographic seizures by methionine sulfoximine pretreatment tightly correlates with the reduction of extracellular taurine in the hippocampus.

Abstract

Initiation and development of early seizures by chemical stimuli is associated with brain cell swelling resulting in edema of seizure-vulnerable brain regions. We previously reported that pretreatment with a nonconvulsive dose of glutamine (Gln) synthetase inhibitor methionine sulfoximine (MSO) mitigates the intensity of initial pilocarpine (Pilo)-induced seizures in juvenile rats. We hypothesized that MSO exerts its protective effect by preventing the seizure-initiating and seizure-propagating increase of cell volume. Taurine (Tau) is an osmosensitive amino acid, whose release reflects increased cell volume. Therefore, we tested whether the poststimulus rise of amplitude of Pilo-induced electrographic seizures and their attenuation by MSO are correlated with the release of Tau from seizure-affected hippocampus. Lithium-pretreated animals were administered MSO (75 mg/kg ip) 2.5h before the induction of convulsions by Pilo (40 mg/kg ip). Electroencephalographic (EEG) power was analyzed during 60 min post-Pilo, at 5-min intervals. Extracellular accumulation of Tau (eTau) served as a marker of cell swelling. eTau, extracellular Gln (eGln), and extracellular glutamate (eGlu) were assayed in the microdialysates of the ventral hippocampal CA1 region collected at 15-min intervals during the whole 3.5-h observation period. The first EEG signal became apparent at ~10min post-Pilo. The EEG amplitude across most frequency bands peaked at ~40 min post-Pilo, and showed strong (r~ .72-.96) temporal correlation with eTau, but no correlation with eGln or eGlu. MSO pretreatment delayed the first EEG signal in Pilo-treated rats by ~10min, and depressed the EEG amplitude across most frequency bands, to values that remained strongly correlated with eTau (r> .92) and moderately correlated (r~ -.59) with eGln, but not with eGlu. Strong correlation between attenuation of Pilo-induced seizures and Tau release indicates that the beneficial effect of MSO is due to the prevention of cell volume increase concurrent with the onset of seizures.