Role of spinal cyclooxygenase (COX)-2 on thermal hyperalgesia evoked by carageenan injection in the rat.
Prostaglandins, which are known to play an important role in the nociceptive transmission in the spinal cord, are produced by cyclooxygenase (COX). Two forms of COX have been identified, COX-1 (constitutive form) and COX-2 (a form highly inducible in response to inflammatory stimuli). COX-2 mRNA was reported to be expressed in the brain in normal rats in the absence of inflammation. We investigated the role of spinal COX-2 in the maintenance of thermal hyperalgesia induced by paw carageenan injection in the rat using NS-398, a selective COX-2 inhibitor. Intrathecally administered NS-398 attenuated the level of thermal hyperalgesia in a dose-dependent manner. This suggested that spinal COX-2 plays an important role in the maintenance of thermal hyperalgesia induced by paw carageenan injection.