“…It has been revealed that NMDA receptor antagonists impaired memory via reduction in nitric oxide level and subsequent cGMP production in the brain [17]. In agreement with our result, both competitive and noncompetitive NMDA receptor antagonists have been reported to impair memory in various behavioral tests [8,17]. Furthermore, although most investigations show memory-impairing effects of NMDA receptor antagonists, there is evidence that at least under some experimental conditions, MK801 can display memory-enhancing properties [4,14].…”