Effects of Papaver rhoeas extract on the development and expression of tolerance to morphine-induced locomotor activity in mice

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 100 mg 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.