A study of the inhibitory effects of nicotine on the expression of morphine-induced conditioned place preference in mice

In the present study, the effects of nicotine on the expression of conditioned place referenced (CPP) induced by morphine in mice have been investigated. Male albino mice (W: 20-25gr) were used in this study and the conditioned place preference was induced by the Carr method. Subcutaneous (s.c) injection of morphine (5 mg/kg) can produce a place preference. Furthermore, intrepretoneal (i.p.) (0.0025, 0.005 and 0.01 mg/kg) and intracerebroventricular (i.c.v) (0.003, 0.1 and 0.3 ng/mice) administration of nicotine significantly decreases the expression of CPP induced by morphine. However, nicotine alone in the mentioned doses doesnt cause motivational effects. It appears that the i.c.v preadministration of the animals with peripheral nicotinic acethyiecholine receptor antagonist, hexamethonium (0.03, 0.1 and OJ mg/mice; 10 min before nicotine) but not with i.p. hexamethonium (1, 5 and 10 mg/kg; 30 min before nicotine), diminishes the effects of nicotine on morphine induced CPP. This result was not observed for the i.c.v and i.p injection of atropine (as muscarinic acethylecholine receptor antagonist). The antagonists themselves, neither showed any motivational effects when used alone nor affected the expression of morphine induced CPP. In conclusion, it appears that central nicotine receptor mechanism(s) may be involved in the expression of the CPP induced by morphine.