The Effects Of Enriched Environment On Morphine Induced CPP And The Levels Of D2 Receptor MRNA In Specific Brain Regions Of High Responsive And Low Responsive Rats

Partâ… : Effects of enriched environment on morphineinduced conditioned place preference in high responsive andlow responsive ratsObjective: To study the effects of enriched environment onmorphine induced place preference in high responsive and low responsiveSD rats, to explore whether enriched environment can affect therewarding effect of morphine in these groups of rats and to what degreedo the different responsive rats react differently to the reward effect ofmorphine.Methods: Male SD rats were used in the experiment 40 days afterbirth. After 7 days of habituation, the rats were classified into high andlow responders in an open field test, depending on whether the locomotoractivity level for the first 10 minutes was on the top third or the bottomthird of the activity score for the subject sample. Then half of the rats ineach group were housing either in an enriched environment or an isolatedenvironment for 42 days, and in the last 12 days of the housing period,half of them were tested in a morphine induced place preferenceprocedure.Results: The EE rats (rats raised in the enriched environment) showed significant reduction of morphine induced place preferencecompared to the IE rats. The high responders both in enrichedenvironment group or the isolated environment group appeared to preferthe morphine paired side more. There was interaction between theenvironmental factor and the inner susceptibility, the high responersraised in the isolated environment showed the most significant morphineinduced CPP.Conclusion: Housing in an enriched environment can attenuatethe rewarding effect of morphine, that may protect individuals from drugabuse. The response of rats in a novel environment can predict thesensitivity to drug of abuse, the high responders may get addicted moresignificantly. The environmental factors and the individual innersusceptibility to addiction affect the addicted behavior together, the onewho are not so susceptible to addiction and being raised in a protectiveenvironment will be not so likely to use drugs of abuse. Partâ…¡: Effects of enriched environment on the D2R mRNAlevels in specific brain regions of addicted or unaddictedhigh responsive and low responsive ratsObjective: To explore the changes of D2 mRNA expression inspecific regions related to drug dependence of addicted or unaddictedhigh responsive and low responsive rats housing in either enrichedenvironment or isolated environment to investigate the possible biologicalmechanisms.Methods: 78 rats which experienced the manipulation in part onewere used in the experiment. All of them were sacrificed and their brainsections were used for the in situ hybridization (ISH) analysis of D2RmRNA levels in field CA1 of hippocampus (CA1), shell of accubensnucleus (AcbSH), prefrontal cortex (PFC) and ventral tegmental area(VTA).Results: The D2R mRNA levels were higher in the enrichedenvironment rats than in the isolated environment rats in AcbSH and PFC,either in addicted group or the unaddicted group, and in the unaddictedgroup, the D2RmRNA levels in EE rats were even higher than that in theblank control group. In PFC, the level of D2R mRNA was lower in thehigh responders than in the low responders from addicted isolatedenvironment, while in AcbSH, the level of D2R mRNA was higher in the high responders than in the low responders from addicted enrichedenvironment.Conclusion: The D2 receptor level was higher in the enrichedenvironment rats than in the isolated environment rats and the blankcontrol group, this suggested that environment may change the dopaminelevel in the brain regions accompanied with behavioral alternations. Insome of the groups, the D2R mRNA level was different between highresponders and low responders, but the trends were different, we couldn'tdetermine whether the relationship between HR and LR in D2R mRNAwas. AcbSH and PFC may be two of the key brain regions of the brainmechanism of environment.