Effects Of Contextual Factors And Small Platform Stress On Morphine-induced Behavioral Sensitization In Mice

Objective (1)To investigate the effects of contextual familiarity on behavioral sensitization induced by chronic morphine administration in mice. (2) To investigate the effects of small platform stress on behavioral sensitization induced by chronic morphine administration in mice.Methods(1)The effects of contextual on morphine behavioral sensitization. Experiment 1: Mice were administrated subcutaneously morphine (10 mg/kg, once per day) for consecutive 7 days either in the test chamber (novel context) or home cage (familiar context). After a 6-day washout period, the mice were challenged with 10 mg/kg morphine and then put into the test chambers to measure their locomotor activity for 1 h. Experiment 2: Mice were administrated subcutaneously morphine (10 mg/kg, once per day) for consecutive 7 days in the test chamber. After a 6-day washout period, the mice were challenged with 10 mg/kg morphine and then put into the test chambers to measure their locomotor activity for 1 h. The paired groups were measured for their locomotor activity in the context in which morphine or saline was administrated, however, the unpaired groups were measured for their locomotor activity in the context in which no morphine or saline was administrated.(2)The effects of small platform stress on morphine behavioral sensitization. Experiment 1: Mice were administrated subcutaneously morphine (10 mg/kg, once per day) for consecutive 7 days in home cage. The MFES team mice put on the small platform (6h, once per day) after 1h. After a 6-day washout period, the mice were challenged with 10 mg/kg morphine and then put into the test chambers to measure their locomotor activity for 1 h. Experiment 2: Mice were administrated subcutaneously morphine (10 mg/kg, once per day) for consecutive 7 days in test chambers. The MPS team mice put on the small platform (6h, once per day) after 1h. After a 6-day washout period, the mice were challenged with 10 mg/kg morphine and then put into the test chambers to measure their locomotor activity for 1 h. The mice were measured for their locomotor activity in the context in which morphine was administrated. Experiment 3: Mice were administrated subcutaneously morphine (10 mg/kg, once per day) for consecutive 7 days in test chambers. The MUPS team mice put on the small platform (6h, once per day) after 1h. After a 6-day washout period, the mice were challenged with 10 mg/kg morphine and then put into the test chambers to measure their locomotor activity for 1 h. The mice were measured for their locomotor activity in the context in which no morphine was administrated.Results(1) The effects of contextual on morphine behavioral sensitization. Experiment 1: Pairing morphine administration to the novel context and the familiar context induced behavioral sensitization in mice. But the degree of behavioral sensitization of the novel context was higher than that of the familiar context. Experiment 2: The expression of behavioral sensitization was only observed in the context in which morphine was administrated.(2) The effects of small platform stress on morphine behavioral sensitization. Experiment 1: The effects of the small platform stress on behavioral sensitization administrated subcutaneously morphine paired with familiar context was no significant. Experiment 2: The small platform stress significant reduced the behavioral sensitization of morphine paired with novel context. Experiment 3: The small platform stress significant increased the behavioral sensitization of morphine unpaired with novel context.Conclusion (1)The induction of morphine behavioral sensitization in mice is related to the contextual familiarity, and this expression of behavioral sensitization is context-dependent. (2)The effects of the small platform stress on behavioral sensitization administrated morphine paired with familiar context was no significant,but the small platform stress destroyed the context-dependent behavioral sensitization.