NMDA RECEPTOR ANTAGONISTS, MK-801 AND ACEA-1011, PREVENT THE DEVELOPMENT OF TONIC PAIN FOLLOWING SUBCUTANEOUS FORMALIN

Subcutaneous injection of formalin produces a biphasic pain response: an early, transient phase followed by a late tonic phase. The present study examined the involvement of the N-methYl-D-aspartic acid (NMDA) receptor in the development of the late pain produced following subcut aneous injection of formalin into the hind paw in mice. Blockade of th e NMDA receptor by its non-competitive antagonist, MK-801, prior to fo rmalin injection, but not after, reduced pain during the late phase. S imilarly, blockade of the NMDA receptor allosteric site by the novel g lycine site antagonist, ACEA-1011, also reduced the pain response in t he late phase. These results suggest that the development of the late phase of formalin pain is due to NMDA-mediated activity during the ear ly phase.