GABAB Receptor Agents into Mesencephalic Cuneiformis of Study of the Effect of Intraperitoneal (i.p) Injection on Metabotropic Naloxone Nucleus(Cnf) of Rat

There are several evidences which prove cuneiformis nucleus involvement in nociception and possible role of opioid modulation of pain transmission from periphery to the cord and other higher nervous centers was the most interest of this study to be justified.

In the present study, the effect of intra cuneiformis microinjection of GABAB receptor agonist (-(-) Baclofen) and antagonists (CGP35348) on morphine-induced antinociception in rat were investigated.

Microinjection of morphine (10µg/0.5µl/rat) or different doses of Baclofen (.25, .5 &1µg per rat) had antinociception in the both, first and second phases of the formalin test. The response induced by morphine or baclofen in both phases was reduced by CGP35348. The response induced by combination of microinjection of baclofen (1µg per rat) and intraperitoneal (i.p) injection of naloxone in both phases was reduced in comparison to saline or baclofen (1µg per rat) alone. Microinjection of CGP35348 alone produced antinociception in the first phase of the formalin test. Morphine in combination with different doses of baclofen did not elicit potentialities in both phases, while CGP35348 in acute phase elicited potentialities.

It may be concluded that Cnf GABAB receptor via opioid receptor, induced antinociception in the formalin test. ***