NMDA AND NON-NMDA RECEPTORS MEDIATING NOCICEPTIVE AND NONNOCICEPTIVE TRANSMISSION IN SPINAL-CORD OF CAT

The effects of excitatory amino acid (EAA) receptor agonists and block ers on the nociceptive and non-nociceptive transmission in cat spinal dorsal horn neurons were studied. About 80% of neurons were facilitate d by iontophoretic injection of EAA receptor agonists (10 - 100 nA), s uch as N-methyl-D-aspartate (NMDA), quisqualic acid (QA), kainic acid (KA), and DL-homocysteic acid (DLH). The nociceptive responses, irregu lar 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). Keta mine and Kyn had different effects on the long-lasting response and th e short-lasting response of neurons induced by stimulation of A affere nt fiber of the tibial nerve. The long-lasting response in 8/12 neuron s was reduced by Kyn, but not by ketamine, and the short-lasting respo nse was reduced by neither Kyn nor ketamine. The DLH-induced excitatio ns were reduced by DNQX and, to a less extent, by APV. The results sug gest that both NMDA and non-NMDA receptors are involved in spinal noci ception; the non-nociceptive information is in part mediated by non-NM DA receptors.