Differential effects of NMDA and non-NMDA receptor antagonists on spinal cutaneous vs muscular nociception in the cat

To investigate the role of glutamate receptor subtypes in spinal transmission of nociceptive cutaneous and muscular afferents, nociceptive responses of WDR neurones in laminae IV-VI of the dorsal horn produced by noxious cutaneous and muscular stimulation were tested in the cat. With microelectrophoretic administration of the NMDA receptor antagonists, 2-amino-5-phosphonovalerate (APV) and ketamine, cutaneous nociceptive responses were preferentially reduced by more than 50%. In contrast, the non-selective excitatory amino acid receptor antagonist kynurenate (Kyn) markedly reduced both cutaneous and muscular nociceptive responses. The difference between APV- and Kyn-induced reductions of muscular nociceptive responses is statistically significant (chi 2-test, p < 0.01). The results suggest that NMDA and non-NMDA receptors preferentially mediate transmission of nociceptive information originating in skin and muscle, respectively.