RESUMO
There are several evidences that show cuneiformis nucleus is involved in nociception. In the present study the effect of intra cuneiformis micro injection of GABA[B] 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 GABA[B] receptor agonist [baclofen] and antagonist [CGP35348] on morphine -iduced antinociception were investigated by formalin test. Microinjection of morphine [l0 micro g /0.5 micro l/saline] or different doses of baclofen [0.25,0.5,1 micro g 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 CGP 35348. The responses induced by combination of baclofen [1 micro g 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 GABA[B] receptor induced antinociception via opioid receptor in the formalin test