INVOLVEMENT OF CHOLINERGIC AND OPIOID RECEPTOR MECHANISMS IN NICOTINE-INDUCED ANTINOCICEPTION

In this work we have studied the influences of nicotinic agents on the antinociception of morphine in formalin test. Nicotine (0.001-0.1 mg/ kg) induced antinociception in mice in a dose-dependent manner in the early phase of formalin test, and also potentiated the morphine effect . The nicotinic receptor antagonist, mecamylamine (0.5 mg/kg), but not hexamethonium decreased the antinociception induced by nicotine (0.1 mg/kg) in both phases. The muscarinic receptor antagonist atropine (5 and 10 mg/kg) also decreased the response of nicotine. Mecamylamine, h examethonium or atropine did not alter morphine antinociceptive respon se, while naloxone decreased responses induced by nicotine or morphine . The antagonists by themselves did not elicit any response in formali n test, however, high doses of mecamylamine tend to increase pain resp onse. It is concluded that central cholinergic and opioid receptor mec hanisms may be involved in nicotine-induced antinociception.