The Effect Of Morphine And Behavioral Sensitization On Impulsive Behavior In Rats

The impulsive behavior is a common feature of different drug addicts.Many studies have shown that human drug abusers are more impulsive than nonusers. Recently, based on the principle of delay discounting in behavioral economics, impulsivity is defined as preference for an immediate but smaller reward rather than a delayed but bigger reward. Researchers have made great progress in the area of alcohol , nicotine, and heroin dependence. .It has been reported that human addicts discount delayed rewards more than nonaddicts, indicating that they are more impulsive. but there is no research about Morphine which is one of the most effective analgesics in clinic to treat postoperative pain or cancer pain. meanwhile, because of the restrict in the research, it is not clear whether this impulsivity reflects preexisting traits, or the effects of exposure to the drug. The animal model give the better method to research impulsivity. This experiment was conducted to study the effect of morphine addiction in the performance of a novel T-maze delayed-procedure. Rats were trained on a T-maze task in which they chose between high and low reward arms, delivery of the high reward was delayed by 15 s. We undertook a study of the effects of acute, chronic morphine exposure and spontaneous withdrawwal on the performance on a test of delayed-procedure. Base on the relation between behavioral sensitization and addiction susceptibility, we also investigate the relationship between impulsivity and morphine-induced behavioral sensitization. This relationship maybe reflect the inducement of impulsivity in drug addiction.Data demonstrate that: the effects of morphine on impulsive choice is significant. and the effect is also influenced by the phase of addiction. Effects of acute injection on impulsive choice is not significant. chronic morphine exposure and spontaneous withdrawwal can significantly increased the rats' preference for an immediate but smaller reward. In the development of behavioral sensitization, there is no significant difference between higher impulsivity group and lower impulsivity group. but in the expression period, the locomotion of higher impulsivity group is significant higher than lower impulsivity group.Conclusions: These results suggested that the direct effects of morphine may contribute to the high level of impulsive behavior. the effect is influenced by the phase of addiction. no difference is found between impulsivity-group and lower impulsivity group in development period of behavioral sensitization,this result indicated that there is no ralationship beween impulsivity and addiction susceptibility. but the significant difference in expression period, may show the relapse in morphine addiction is influenced by impulsivity.