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Effects of morphine on acquisition and retrieval of memory have been proven in the avoidance paradigms.In present study,we used a two-trial recognition Y-maze to test the effects of acute morphine and morphine withdrawal on spatial recognition memory.Y-maze is based on the innate tendency of rodents to explore novel environments therefore can avoid punishment and reward.Results:1) Pre-training morphine 10 mg/kg impaired the recognition spatial memory of acquisition after a 1 h inter-trial interval (ITI),whereas morphine 2.5,5 and 10 mg/kg showed impairment after 2 h ITI.2) Preretention morphine 5,10 mg/kg disrupted the retrieval of memory after 1 h ITI.3) Morphine 5 and 10 mg/kg caused hyperlocomotor activity depending on the state.4) Mice withdrawn from morphine 40 mg/kg but not 10 mg/kg for 3 d showed anmesia in Y-maze.Our data suggested t hat acute morphine impaired the acquisition and retrieval of spatial recognition memory and increased the locomotor activity in Y-maze depending on the dose and state.Moreover,withdrawal from chronic morphine also impaired acquisition in Y-maze depending on the dose and state.