Rich Environment And Stress On The Effects Of Morphine Behavioral Sensitization In Mice

Drug addiction refers to the addicts’strong physical and psychological dependence on drugs, compulsive drug-seeking and drug-use behavior. Only a small percentage of people who have experienced drug develop the compulsive pathological syndrome that is typical of drug addiction. The addiction susceptibility of organism is not only affected by gene and heredity, but also suffering from environmental factors. Positive postnatal environment can improve the extent of drug addiction, and enriched environment is a good simulation of positive environmental factors in human life, thus the role of the enriched environment gains increasing attention in recent years. Most research results show that enriched environment can improve drug addiction in behavioral and neurochemical aspects. Many studies have shown that the effect of enriched environment on drug addiction is closely related to the level of stress, but till now there’s no combined research of enriched environment, stress and drug addiction.In this study, the effect of the environment and restraint stress on stress level and morphine behavioral sensitization in mice was investigated.60mice were divided into five groups, in which they were treated with their respect level of environment and stress. After two months of environment treatment, mice were tested in the elevated plus maze and morphine behavioral sensitization. The results show that (1) enriched environment significantly reduces the stress level of the mice in the elevated plus maze test,(2)also significantly reduced spontaneous activity in acute morphine treatment and the saline-induced relapse test, but no environmental treatment effect in morphine-induced relapse test was found.(3) Correlation analysis shows a high correlation of stress level and morphine behavioral sensitization.(4) Restraint stress did not significantly change the performance of animals either in the elevated plus maze or morphine behavioral sensitization.The results indicate that (1) enriched environment can reduce the stress level of animals.(2) Enriched environment has a very good preventive effect on acute morphine (5mg/kg) treatment as well as context-induced relapse of morphine, but the effect is not that strong enough to change the relapse induced by morphine.(3) The animal’s stress level can, to some extent, predict acute morphine addictive susceptibility and the relapse induced by context.(4) In this study, the effect of chronic mild restraint stress is not strong enough to change the animal’s stress level and morphine addiction.