(+)-MK 801 is a potent antagonist of NMDA with Ki value of 30.5nM . MK 801 is a potent anticonvulsant exhibits both anxiolytic and sympathomimetic properties. It is found to be a noncompetitive antagonist of NMDA. MK 801 can penetrate into the central nervous system. In the in vitro assay, MK 801 binds to rat cerebral cortical membrane with high affinity in a saturable manner. This binding is reversible even when the concentration of MK 801 is up to 100μM. It is also found that the binding shows a regional specificity. Most of these binding sites are located in the hippocampus. In rat cortical-slice preparations, MK 801 causes a potent blockade of depolarizing responses to NMDA with a high selectivity. This effect is persistent. The blockade can also cause a suppression of the epileptiform activity induced by tetrodotoxin or other neurotoxin .