The effect of antagonists on N-methyl-d-aspartate (NMDA)-induced response was investigated in isolated nucleus tractus solitarii (NTS) neurons freshly isolated from the rat using a conventional patch-clamp technique. The NMDA-induced inward current consisted of an initial peak followed by a steadystate component. The competitive antagonists of NMDA receptor, d-2-amino-5-phosphonovalerate (APV), d-2-amino-4-phosphonoheptanoate (APH) and 3-3(2-carboxypiperazine-4-yl)propyl-1-phosphate (CPP), selectively suppressed the initial peak of NMDA-induced current more than the steady-state component at low concentrations. The non-competitive antagonists, MK-801, ketamine, Zn2+ and Mg2+, equally blocked both peak and steady-state components.
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