DIFFERENT METHODS OF ASSESSING NICOTINE-INDUCED ANTINOCICEPTION MAY ENGAGE DIFFERENT NEURAL MECHANISMS

Two methods were used to assess nicotine-induced antinociception: tail withdrawal from a hot water bath and hind paw withdrawal from a hotpl ate. Nicotine doses which produced 75-80% maximum response were 0.75 m g/kg (free base) for tail withdrawal and 0.35 mg/kg for paw withdrawal . The peripheral blocker chlorisondamine (0.1 mg/kg, SC) and the centr al antagonist, mecamylamine (1 mg/kg, SC) were each effective in block ing nicotine-induced increases in tail withdrawal latencies, suggestin g that this effect of nicotine depends on either the action of nicotin e at peripheral receptors or the functional integrity of those recepto rs. In contrast, nicotine-induced increases in paw withdrawal latencie s were blocked by mecamylamine but not by chlorisondamine, even at oth er agonist/antagonist dose combinations. The results indicate that the se two effects of nicotine involve at least partially separate pathway s and may reflect a different mix of the antinociceptive and motor dep ressing effects of nicotine.