Ethanol-Induced Antinociception in Rodents: Role of the Cholinergic and Opioidergic Systems

We examined antinociceptive properties of ethanol and the mechanism of its action using two thermal (hot-plate and tail-flick) and two chemical (acetic acid-induced writhing and formalin) nociception tests. The mechanism of antinociception was analyzed using naloxone (an opioid antagonist) and atropine (a cholinergic blocker). It was found that ethanol in a dose-dependent manner produced significant ( P < < 0.05) prolongations of both the hot-plate and tail-flick latencies. In the chemical tests, ethanol caused a significant ( P < 0.05) reduction in the number of writhings produced by acetic acid and also a significant decrease ( P < 0.01) in the licking time produced by formalin within both phases of the respective test. It was also observed that both atropine and naloxone significantly ( P < 0.05) suppressed ethanolinduced antinociception effects. We conclude that the antinociceptive action of ethanol may in part be opiodergic- and cholinergic-dependent.