title: Nicotine-induced antinociception in rats and mice: correlation with nicotine brain levels.
abstract: Nicotine was found to be potent in producing antinociception in mice and rats as measured by tail-flick latency but its action was of short duration. Nicotine's ED50 values (confidence limits) were 0.7 (0.4-1.1) and 2.0 (1.2-3.4) mg/kg in rats and mice, respectively, at the time of maximum effect. Brain levels of nicotine reached a maximum at 10 min, whereas antinociception was maximal within 2 min in rats. However, there was a good correlation between the time courses of antinociception and brain levels of nicotine in mice with both attaining maximal levels at 5 min. It was found that tachyphylaxis developed to the antinociception in rats within 10 min and lasted for up to 14 h, but tachyphylaxis did not develop to nicotine-induced antinociception in mice. The effect of nicotine appeared to be central in both rats and mice inasmuch as mecamylamine antagonized completely but hexamethonium (5 mg/kg) antagonized partially. Nicotine-induced antinociception was not blocked in either rats or mice by atropine in doses up to 10 mg/kg. Naloxone did not block nicotine in rats but did antagonize the antinociception in mice. In addition, yohimbine, a selective alpha-2 antagonist, blocked the antinociception in both species. These data implicate several different mechanisms in the antinociceptive action of nicotine.
mesh_terms: D000700:Analgesics; D000818:Animals; D001921:Brain / Q000378:metabolism*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009538:Nicotine / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000187:drug effects; D013045:Species Specificity; D013618:Tachyphylaxis; D013997:Time Factors
chemical_list: D000700:Analgesics; D009538:Nicotine