The Role Of D3R And Expression Of D1R-D5R Gene In Methamphetamine-induced Behavioral Sensitization In Mice

Objective:To study the regulation of dopamine D3 receptor（D3R）and the changes of gene expression in methamphetamine-induced behavioral sensitization of mice,and to explore the gene expression characteristics of dopamine receptor subtypes in different brain regions and their roles in METH addiction.This study laid a foundation for further elucidating the molecular biological mechanism of METH addiction.Methods:（1）Establishment of behavioral sensitization model of mice induced by METH:All experimental mice were divided into four groups:wild type mouse saline group（WT SA group）,wild type mouse METH group（WT METH group）,D3R gene knockout mouse METH group(D3R^-/-SA group),and D3R gene knockout mouse METH group(D3R^-/-METH group).The experimental process includes four stages:pretest,formation,transformation and expression.（2）In this study,the four types of brain nuclei,namely prefrontal cortex（PFc）,nucleus accumbens（NAc）,caudate putamen（CPu）and hippocampaus（Hip）,which are closely related to drug addiction,were used as the subjects.After the behavioral test,all mice were killed after dislocation of cervical spine,and four kinds of nuclei were isolated rapidly.The expression level of each gene was calculated by using quantitative real-time polymerase chain reaction.All data were expressed by mean±SEM.P<0.05 was the statistical significance standard.Results:（1）Effect of METH on behavioral sensitization in mice:After METH（2.0 mg/kg）injection,mice of both genotypes showed significantly increased voluntary activity and persistent behavioral sensitization（P<0.05）,suggesting that METH abuse can lead to addiction.However,the autonomous activity of D3R^-/-mice was significantly lower than that of corresponding WT mice（P<0.05）,suggesting that D3R activation may play a positive regulatory role in METH addiction.（2）Expression changes of five DA receptor（D1R–D5R）genes in different brain regions:There were significant differences in the distribution of the five types of DR in different brain regions,that is,among the nuclei of the four brain regions,D1R and D2R were more distributed in NAc and CPu,while D3R was more distributed in NAc,while D4R and D5R showed no significant differences in the distribution of their expressions.Statistical analysis showed that the expression of five dopamine receptors in different brain regions was different.Compared with SA group,the expression of D1R and D2R in NAc and CPu of WT mice decreased（P<0.05）,and the expression of D1R and D2R in CPu of D3R^-/-mice decreased（P<0.05）;the expression of D3R in PFc,NAc and Hip of WT mice increased（P<0.05）;there were no significant changes in D4R and D5R in WT mice（P>0.05）.These results suggest that these receptor subtypes,especially D1R,D2R and D3R,may be synergistically involved in regulating METH addiction.Conclusion:（1）Repeated and persistent METH effects can induce behavioral sensitization in mice,suggesting that METH abuse can lead to addiction.Behavioral and gene expression results suggest that D3R activation may play a positive regulatory role in METH addiction.（2）The expression distribution of D1R–D5R is significantly different in different brain regions.After METH action,these receptor subtypes,especially D1R,D2R and D3R,may cooperate in regulating METH addiction.