NMDA and non-NMDA receptors mediating nociceptive and non-nociceptive transmission in spinal cord of cat

The effects of excitatory amino acid (EAA) receptor agonists and blockers on the nociceptive and non-nociceptive transmission in cat spinal dorsal horn neurons were studied. About 80% of neurons were facilitated by iontophoretic injection of EAA receptor agonists (10-100 nA), such as N-methyl-D-aspartate (NMDA), quisqualic acid (QA), kainic acid (KA), and DL-homocysteic acid (DLH). The nociceptive responses, irregular spontaneous discharges, and C afferent induced-response of dorsal horn neuron, were reduced by the different EAA receptor blockers (35-150 nA), such as DL-2-amino-5-phosphono-valerate (APV), ketamine, 6,7-dinitro-quinoxaline-2, 3-dion (DNQX), and kynurenic acid (Kyn). Ketamine and Kyn had different effects on the long-lasting response and the short-lasting response of neurons induced by stimulation of A afferent fiber of the tibial nerve. The long-lasting response in 8/12 neurons was reduced by Kyn, but not by ketamine, and the short-lasting response was reduced by neither Kyn nor ketamine. The DLH-induced excitations were reduced by DNQX and, to a less extent, by APV. The results suggest that both NMDA and non-NMDA receptors are involved in spinal nociception; the non-nociceptive information is in part mediated by non-NMDA receptors.