THE INHIBITION OF MELATONIN ON RELAPSE BEHAVIOR IN MORPHINE-DEPENDENT RATS

Objective: To study the inhibitory efficacy of melatonin (Mel) on relapse behavior in morphine-dependent rats. Methods: Morphine was administered via subcutaneous injection at gradually increasing doses (from 10 mg·kg -1 to 60 mg·kg -1 ) for 6 days to establish morphine conditioned place preference(CPP). From Day 7, the rats were administered saline instead of morphine for 10 days to induce CPP extinction. The rats then were given a single priming injection of morphine 4 mg·kg -1 to reinstate the morphine CPP. Some rats were treated by ip melatonin (20, 40 and 80 mg·kg -1 ) prior to priming injection of morphine. Results: After priming injection of morphine 4 mg·kg -1 , the time spent on the drug-paired side was significantly reduced because of the treatment with Mel(40 and 80 mg·kg -1 ), compared with Mor Group P0 05, P0 01. No significant statistical differences were observed between Mor Group and Mel 20 Group (P 0 05). Conclusion: Mel has some effects on the inhibitory of relapse behavior induced by priming injection of morphine in morphine-dependent rats.