the fruit essential oil of cuminum cyminum l. reduced the acquisition but not expression of ineffective dose of morphine-induced conditioned place preference in morphine- sensitized mice

background: cuminum cyminum fruit essential oil (feo) dose-dependently can attenuate the expression of morphine tolerance and dependence in morphine-dependent mice. objective: in this study, the effects of cuminum cyminum feo on acquisition and expression of morphine-induced conditioned place preference (cpp) in morphine-sensitized mice were studied. methods: repeated subcutaneous (s.c.) administration of morphine (5 mg/kg), once daily for three and 5 days free of the opioid (sensitization period), increased conditioning response induced by ineffective doses of morphine (0.25, 0.5 and 0.75 mg/kg). results: the results showed that intra-peritoneal (i.p.) injection of cumin feo (0.001, 0.01, 0.1, 0.5, 1 and 2% 5 ml/kg) or tween-80 (0.5% 5 ml/kg), 60 min before administration of morphine or saline during sensitization period (acquisition), decreased the conditioning response induced by ineffective dose of morphine (0.5 mg/kg s.c.) at the doses of 1% (p<0.05) and 2% (p<0.001) while cumin feo (0.001-2% i.p.), just 60 min before the test on post-conditioning phase (expression experiments), did not alter the conditioning scores in morphine- and non-sensitized mice. conclusion: our findings showed that the cuminum cyminum fruit essential oil reduces the acquisition but not expression of morphine-induced conditioned place preference in morphine-sensitized mice.