Contribution of the Nucleus Cuneiformis to the Antinociceptive Effects of Systemic Morphine on Inflammatory Pain in Rats

• Main Authors: Abdolaziz Ronaghi, Mohammad Ebrahimzadeh, Abbas Haghparast
• Format: Article
• Language: English
• Published: Iran University of Medical Sciences 2011-10-01
• Series: Basic and Clinical Neuroscience
• Subjects: Nucleus Cuneiformis; Electrolytic Lesion; Reversible Inactivation; Morphine; Formalin Test; Rat.
• Online Access: http://bcn.iums.ac.ir/browse.php?a_code=A-10-1-89&slc_lang=en&sid=1
• ISSN: 2008-126X; 2228-7442

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.