1 Opioid receptors in the brain activate descending pain pathways to inhibit the nociceptive response to acute noxious stimuli. The aim of the present study was to clarify the role of supraspinal opioid receptors in modulating the nociceptive response to persistent in¯ammation in rats. 2 Subcutaneous administration of 50 ml of complete Freund's Adjuvant (CFA) into the plantar surface of the hindpaw induced a signi®cant decrease in paw withdrawal latency to thermal stimuli (P50.01) at 24 h post-injection. 3 Intracerebroventricular (i.c.v.) administration of the m opioid receptor agonists, DAMGO and morphine, and the d opioid receptor agonists, deltorphin II and SNC80, signi®cantly reversed the hyperalgesic response associated with peripheral in¯ammation in a dose-dependent manner (P50.0001). 4 The m and d agonists also signi®cantly attenuated the antinociceptive response to acute thermal stimulation in rats (P50.001). However, deltorphin II and SNC80 were less potent, and in the case of SNC80 less e cacious, in modulating the response to acute thermal nociception in comparison to hyperalgesia associated with persistent in¯ammation. 5 These results indicate that m and d opioid receptors in the brain modulate descending pain pathways to attenuate the nociceptive response to acute thermal stimuli in both normal and in¯amed tissues. The heightened response to d agonists in the hyperalgesia model suggests that d opioid receptors in the brain are promising targets for the treatment of pain arising from chronic in¯ammation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.