Contribution of the nucleus cuneiformis to the antinociceptive effects of systemic morphine on inflammatory pain in rats

Introduction: the role of midbrain reticular formation, which includes the nucleus cuneiformis (ncf), as a crucial antinociceptive region in descending pain modulation has long been investigated. in this study, we tried to highlight the role of ncf in morphine-induced antinociception in formalin-induced pain model in rats. methods: a total of 201 male wistar rats weighing 260-310 g were used in this study. the effective dose of morphine in systemic administration (intraperitoneal; i.p.) was determined after a dose- and time-response protocol. in consequent groups, bilateral electrolytic lesion (500 μa, 30 sec) or reversible inactivation (lidocaine 2%) were used in the ncf before systemic administration of morphine, and then, the nociceptive test was immediately carried out. results: the results showed that administration of 6 mg/kg morphine, 30 min before the formalin test, is the best dose- and time-response set in these experiments. the obtained data also indicated that bilateral electrical destruction or reversible inactivation of the ncf significantly decreased antinociceptive responses of systemic morphine (6 mg/kg; i.p.) during the second phase of formalin test (p<0.05). discussion: therefore, it seems that opioid receptors located in the ncf may be involved in modulation of central sensitization which occurred in inflammatory pain in rats.