The NMDA receptor: central role in pain inhibition in rat periaqueductal gray.

An injection of the excitatory amino acid analogue, N-methyl-D-aspartate (NMDA), in the rat periaqueductal gray resulted in potent analgesia. A prior injection of the NMDA antagonist, (-)-2-amino-7-phosphonoheptanoate (D-AP7), antagonized this action, indicating a receptor-mediated action. NMDA given with morphine potentiated the morphine analgesia while D-AP7 blocked morphine analgesia. These results delineate for the first time a functional role for the NMDA receptor in the control of pain in the mammalian central nervous system.