Fig. (1) The NMDA receptor complex Glutamate and NMDA bind to the agonist site on NMDA receptors. Phencyclidine (PCP), ketamine, and dizocilpine ((+)-MK-801) bind to PCP-receptor in the inside of the NMDA receptors. Glycine and D-serine bind to co-agonist site (glycine modulatory site) on the NMDA receptors.