Objective: Neuroprotective, antioxidant, anticonvulsant, and analgesic effects of Nigella sativa (NS) have been previously shown. The interaction of NS with opioid system has also been reported. In the present study, the effects of NS hydro-alcoholic extract on the acquisition and expression of morphine-induced conditioned place preference (CPP) in rats were evaluated.
Materials and methods: CPP was induced by injection of morphine (5 mg/kg, i.p.) on three consecutive days in compartment A of the CPP apparatus. Injection of NS extract (200 and 400 mg/kg, i.p.) 60 min before morphine administration on the conditioning days and 60 min before the post-conditioning phase was done for the evaluation of acquisition and expression effects, respectively. Conditioning effect of NS extract was also evaluated by injection of extract (200 or 400 mg/kg, i.p.) in the conditioning phase, instead of morphine in different groups. The difference in time which the animals spent in compartment A on the day before conditioning and the days after conditioning was determined and compared between groups.
Results: The time spent by the rats in compartment A in the morphine group was greater than that in the saline group (P < 0.01). Both doses of NS extract decreased acquisition of morphine-induced CPP (P < 0.01 and P < 0.001), but had no significant effect on the expression of morphine CPP. Higher dose of the extract (400 mg) showed a significant conditioning effect which was comparable to the effect of morphine.
Conclusion: The results of the present study showed that the hydro-alcoholic extract of NS has conditioning effect. It also decreased acquisition, but had no significant effect on the expression of morphine CPP.
Keywords: Conditioned place preference; Nigella sativa; morphine; rat.