Abstract: Aim To study theEffects of scoplamine, a marscarinicreceptor antagonist on intravenous morphine self-administration and reinstatement of responding in rhesus monkeys (fixed ratio 1, FR1).Methods Rhesus monkeys were trained to press response lever for intravenous morphine self-administration under a fixed ratio 1 schedule in a daily 4 h session.Response pattern, total responserate, total mophine intake and spontaneous activity wererecorded duringsessions.Effects of acute pre treatment with different doses of scopolamine on self-administration were studied, and alson theEffects of acute and chronic treatment with scopolamine on reinstatement of responding by priming dose of morphine were observed afterext inction of self-administration were observed.Results Theresul ts showed that acute treatment of scopolamine (0.025 ~ 0.75 mg/kg)could not only attenuate intravenous morphine self-administration under a F R1 schedule, which was represented by decreased total morphine intake and responserate persession, but also delay theinitiation of morphine self-administration.Theresponse pattern was affected under this treatment.Chronic Effect of scoplamine was also evaluated afterext inction during which a daily dose of scopolamine(0.25 mg/kg)was administered, andin thetesting day, only a priming dose of morphine (0.25 mg/k g)was administered.Chronic scopolamine treatment caused 45 % decrease of responserate by morphine priming.Conclusion Chronic scopolamine treatment might inhibitthereinstatement of responding afterextinction.

Key words: scopolamine, morphine, self-administration, reinstatement