Effect of GABAB Agonist and Antagonist Microinjection into Cuneiformis Nucleus (CNF) on Morphine Induced Antinociception by Formalin Test in Rat

There are several evidences that show cuneiformis nucleus is involved in nociception. In the present study the effect of intra cuneiformis microinjection of GABAB agonist (baclofen) and antagonist (CGP35348) on morphine induced antinociception in rat were investigated. In this expremental study, through canulation of cuneifoprmis nucleus in rat the effect of intra cuneiformis (CNF) microinjection of GABAB receptor agonist (baclofen) and antagonist (CGP35348) on morphine – iduced antinociception were investigated by formalin test. Microinjection of morphine (10μg /0.5 μl/saline) or different doses of baclofen (0.25,0.5,1μg per rat) had antinociception in the both first and second phases of formalin test. The response induced by morphine or baclofen in both phases were reduced by CGP35348. The responses induced by combination of baclofen (1μg per rat) and intraperitoneal (ip) injection of naloxan were reduced in both phases of formalin test. Microinjection of CGP35348 alone has produced antinociception in first phase of the formalin test. Morphine with different doses of baclofen did not increase the antinociception effect whereas microinjection of CGP35348 administration significantly increased the antinociception in acute phase. It may be concluded that CNF GABAB receptor induced antinociception via opioid receptor in the formalin test.