Mechanistic Insight into the Attenuation of Initial Pilocarpine-Induced Seizures in Young Rats by a Non-Convulsive MSO Dose

Pretreatment with non-convulsive dose of methionine sulfoximine (MSO) attenuated lithium-pilocarpine-induced (Li-Pilo) seizures in young rats [1]. We hypothesized that the effect of MSO results from a) glutamine synthetase block-mediated inhibition of conversion of Glu/Gln precursors to neurotransmitter Glu, and/or from b) altered synaptic Glu release. Pilo was administered 60 min prior to sacrifice, MSO at 75 mg/kg, i.p., 2.5 h earlier. [1,2-13C]acetate and [U-13C]glucose were i.p.injected either together with Pilo (onset) or 15 min before sacrifice (final phase). Their conversion to Glu and Gln in hippocampus and entorhinal cortex was followed using [13C] gas chromatographymass spectrometry. Release of in vitro loaded [3H]D-Asp from ex vivo brain slices was measured in continuously collected superfusates. Protein and mRNA expression were measured by Western Blot and real-time PCR techniques, respectively. At no time point nor brain region did MSO modify incorporation of [13C] to Glu or Gln in Pilo-treated rats. MSO pretreatment decreased by ~37% high potassium-induced [3H]D-Asp release and reduced by ~50% the synaptic vesicular Glu transporter VGLUT1 protein, but not mRNA content in the hippocampus. The results indicate that MSO at nonconvulsive dose mitigates the initial Pilo-induced seizures by interfering with synaptic Glu-release but not with neurotransmitter Glu recycling.