ROLE OF THE EXCITATORY AMINO-ACID RECEPTORS IN THE MEDIATION OF THE NOCICEPTIVE RESPONSE TO FORMALIN IN THE RAT

The relative contribution of the NMDA/glycine allosteric site and non-NMDA (AMPA) types of glutamate receptor to the acute and tonic phases of the behavioural nociceptive response to formalin has been studied in the rat. The AMPA receptor selective antagonist NBQX preferentially inhibited the acute phase indicating that AMPA receptors may be involved in mediating fast acute nociceptive transmission in the dorsal horn. In contrast, the strychnine-insensitive glycine site partial agonist (+)-HA-966 and the NMDA competitive antagonist CGS 19755 preferentially attenuated the tonic nociceptive phase. However, none of these compounds exhibited anti-inflammatory properties. Thus, both NMDA and non-NMDA antagonists can selectively block changes in neuronal excitability while tissue injury in the receptive field continues to evolve.