Involvement of unusual glutamate release in kainate-induced seizures in zinc-deficient adult rats.

Enhanced susceptibility to kainate-induced seizures is linked to a lack of increase in GABA release in zinc-deficient young rats. In the present study, susceptibility to kainate-induced seizures was examined in adult (12-week-old) rats fed a zinc-deficient diet for 4 weeks to evaluate the relationship between the dysfunction of GABAergic neurotransmitter system and seizure susceptibility in zinc deficiency. Susceptibility to kainate-induced seizures was enhanced in zinc-deficient adult rats. Extracellular glutamate concentration in the hippocampus was markedly (>2 times) higher in zinc-deficient adult rats than in the control before and after treatment with kainate. Extracellular zinc concentration in the hippocampus was also higher in zinc-deficient adult rats. Interestingly, it was decreased in both zinc-deficient and control rats after treatment with kainate. In some zinc-deficient adult rats, extracellular GABA concentration in the hippocampus was increased with extracellular glutamate concentration after treatment with kainate. When the capacity for GABA release was examined by excessive stimulation with 100mM KCl, extracellular GABA concentrations were significantly increased even in zinc-deficient adult rats. These results suggest that GABA can be excessively released in zinc-deficient adult rats. An unusual glutamate release may be involved in the enhanced susceptibility to kainate-induced seizures in zinc-deficient adult rats.