Cholinergic mechanism in imipramine and morphine antinoception.

Antinociceptive effect of imipramine and morphine was studied in rats using tail flick method. Morphine and imipramine both increased the latency of tail flick response. Pretreatment with naloxone (0.5 mg kg-1) decreased the antinociceptive effect of morphine (1 mg kg-1) and imipramine (10 mg kg-1). In order to see if antinociceptive effect of morphine or imipramine involve cholinergic mechanisms, mecamylamine (1 mg kg-1) or atropine (1 mg kg-1) were administered 30 minutes before morphine (1 mg kg-1) or imipramine (10 mg kg-1) administration. Mecamylamine decreased the antinociceptive effect of morphine and imipramine (P < 0.001), whereas atropine had no effect. Thus, opiodergic and nicotinic systems appear to be involved in morphine and imipramine induced antinociception.