Antinociceptive effects of central and systemic administrations of nicotine in the rat.

Nicotine (0.16--0.50 mg/kg, SC) was found to exert a potent antinociceptive action on thermal stimuli as measured by the tail-flick test. This antinociceptive action of nicotine could be blocked by centrally active nicotinic or muscarinic blockers implicating both classes of cholinergic receptors in this effect. Quaternary blockers, however, failed to prevent nicotine-induced antinociception. This finding, together with the ability of small doses of nicotine (25 micrograms) to induce potent antinociceptive effects when administered centrally, suggests a central site of action for the antinociceptive action of nicotine. The present results also support the suggestion that nicotine may selectively reduce sensitivity to certain classes of pain stimuli, perhaps through a central releasing action on acetylcholine.