Methylmercury Increases Glutamate Release from Brain Synaptosomes and Glutamate Uptake by Cortical Slices from Suckling Rat Pups: Modulatory Effect of Ebselen

During the early postnatal period the brain is extremely sensi- tive to external agents. Here, we examined the effect of subcuta- neous injections of methylmercury (MeHg; 2 mg/kg) during the suckling period (postnatal days (PND) 3-10, 3-17, or 3-24) on glutamate release from brain synaptosomal preparations and on glutamate uptake by brain cortical slices of rat pups. The possible antagonist effect of ebselen against MeHg effect was also exam- ined at PND 24. MeHg increased the basal (but not K-stimu- lated) glutamate release and glutamate uptake at PND 24. A strong tendency of increase in the basal glutamate release from synaptosomes (p 0.088) was observed at PND 17. Ebselen, which did not affect glutamate release and uptake per se, prevented both effects of MeHg. This study indicates that (1) the effect of MeHg on glutamate release could be involved in its toxicity; (2) the increase in the glutamate uptake could represent a pathophysio- logical response to MeHg-induced glutamate release; (3) the in- hibitory effect of ebselen on MeHg-induced glutamate release could be related to its reported neuroprotective effects.