Autumn 2011, Volume 3, Number 1 35 Basic and Clinical 1. Introduction t is well established that systemic administra- tion of morphine produces antinociception in part through the activation of supraspinal sys- tems that inhibit spinal nociresponsive neu- rons through descending projections (Yeung & Rudy, 1980). The antinociceptive effects of mor- phine and related compounds on formalin-induced pain Contribution of the Nucleus Cuneiformis to the Antinociceptive Effects of Systemic Morphine on Infammatory Pain in Rats Abdolaziz Ronaghi, Mohammad Ebrahimzadeh, Abbas Haghparast* Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, Tehran, Iran. I * Corresponding Author: Abbas Haghparast, PhD. Neuroscience Research Center, Shahid Beheshti University of Medical Sciences, P.O. Box 19615-1178, Tehran, Iran. Tel./fax: +98- 21 -22431624 E-mail: Haghparast@yahoo.com 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 signifcantly 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 infammatory pain in rats. A B S T R A C T Article info: Received: 10 August 2011 First Revision: 20 August 2011 Accepted: 8 September 2011 behaviors have already been demonstrated. Systemic morphine inhibited both the early and late phases of the formalin-induced licking responses, and this action was naloxone-sensitive (Dubuisson & Dennis, 1977; Oluyo- mi, Hart, & Smith, 1992) as well. It has been shown that wide variety of brain regions including the frontal lobe, anterior cingulate cortex, insula, amygdala, hypothalamus, periaqueductal gray Key Words: Nucleus Cuneiformis, Electrolytic Lesion, Reversible Inactivation, Morphine, Formalin Test, Rat. Downloaded from http://journals.tums.ac.ir/ at 5:17 IRST on Monday October 8th 2012