Abstract

In the current study, effects of a water-alcohol extract of Papaver rhoeas L.(Papaveraceae) on the acquisition and expression of morphine-induced behavioral tolerance in mice was investigated. Subcutaneous (s.c.) administration of morphine (50 mg/kg) induced locomotor activity in animals. Reduction of locomotor behavioral response in mice pretreated with morphine (50 mg/kg, twice daily for 3 days) alone indicates that tolerance had been developed. Extract (25, 50, and 100mg/kg, i.p.) administration, 30 min before each of three daily doses of morphine, augmented the development of tolerance. Moreover, intraperitoneal administration of the plant extract (25, 50, and 100 mg/kg) 30 min before the test inhibited the expression of morphine-induced behavioral tolerance. The results indicate that administration of the extract of Papaver rhoeas induces different effects on the acquisition and expression of morphine-induced behavioral tolerance in mice.