Effects of a Rhodiola rosea L. extract on the acquisition, expression, extinction, and reinstatement of morphine-induced conditioned place preference in mice

RATIONALE: Opioid addiction is a chronic, recurrent brain disease that is characterised by compulsive drug seeking and a high rate of relapse even after long periods of abstinence. Prevention of relapse is the primary goal of addiction treatment and is still the major limitation in drug therapy. OBJECTIVES: The present study investigated the effects of a Rhodiola rosea L. hydroalcoholic extract (RHO), a well-known traditional oriental medicine, on establishment and reinstatement of morphine-induced conditioned place preference (CPP) in mice. METHODS: CPP was induced by intraperitoneal injection of morphine (10 mg/kg) as an 8-day conditioning schedule. The effects of RHO on the rewarding properties of morphine were tested in mice receiving oral administration of RHO (10, 15, and 20 mg/kg) 60 min prior to each morphine injection (acquisition) or prior to the CPP test on day 9 (expression). Once established, CPP was extinguished by repeated testing, during which conditioned mice were injected daily with different doses of RHO. Finally, the efficacy of RHO in blocking reinstatement of CPP provoked by priming injections and physical stress was also evaluated. RESULTS: RHO administration showed dose dependency for prevention of establishment of CPP and was effective in facilitating extinction of morphine-induced CPP. RHO suppressed both priming- and stress-induced reinstatement of CPP in a dose-dependent manner. CONCLUSIONS: In conclusion, as RHO was effective for reducing craving and vulnerability to relapse, it might be a very effective natural remedy for the treatment of opioid addiction.