L-NAME modulates glutamate accumulation induced by K(+)-depolarization but not by forebrain ischaemia in the rat...

The accumulation of extracellular glutamate and aspartate in the striatum of rats during ischaemia was examined by perfusion with Ca(+)-free medium and treatment with the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). Male Wistar rats were subjected to 30 min ischaemia using the 4-vessel occlusion model or high K(+)-depolarization. Extracellular glutamate and aspartate were monitored by in vivo microdialysis. Perfusion with Ca(2+)-free medium and systemic administration or local perfusion of L-NAME reduced the K(+)-evoked glutamate accumulation but not the ischaemia-induced glutamate accumulation. The aspartate concentration was unaffected in both conditions. Our data suggest that the extracellular glutamate and aspartate originates from a Ca(2+)-independent pool during forebrain ischaemia and is not modulated by nitric oxide. In high K(+)-depolarization the accumulated glutamate may arise, at least in part, from enhanced vesicular release and is modulated by nitric oxide.