The role of dopamine D2 receptor and transporter in the different susceptibility of morphine-induced conditioned place preference in rats

Abstract

Objective To investigate the expression of dopamine D2 receptor(D2 R)and dopamine transporter(DAT)located in the medial prefrontal contex(mPFC)in high and low CPP rats,thus to unveil the possible mechanism lead to the different CPP susceptibility.Methods 160 male Sprague-Dawley rats were randomly assigned into experiment group (n=130)and control group(n=30).The experiment group were re-classified into two groups according to the numerical value of the CPP(Conditioned place preference):high preference group(HP group)and low preference group(LP group).Further,according to the executed time-points after the last administration.each the HP and LP group was classified into 3-holly group(3H),72-hour group(JD3)and 14-day group (JD14)respectively.At the time of 3 hours,72 hours and 14 days after the final injection,rats were scarified and cardio-perfused,and the brains were removed and sliced up coronarily.The mRNA levels of D2R and DAT in mPFC were estimated with in situ hybridization.Results No significant difference of pretest scores staying at the non-preference chamber exist among the three groups(P＞0.05),however,the test scores of the CPP minus the time stayed at pretest natural preference in the HP group was significantly higher than the LP group(P＜0.01).In 3H,J3D and J14D group,the expression of D2R mRNA in HP group(125.43±2.90～142.92±3.32)were lower that of in LP group(122.25±2.20～136.67±5.39),and the difference between the HP and LP group was significant(P＜0.01).In 3H and J3D,the expression of DAT mRNA in HP group(157.00±3.55～145.15±3.69)were significantly lower than that of in LP group(150.69±3.12～138.84±3.99)(P＜0.01).In J14D,there were no difference between 3 groups in mPFC(P＞0.05).Conclusions It can be inferred that D2R and DAT maybe correlated closely and underlie the different susceptibility to morphine induced CPP. Key words: Morphine; Psychological dependence; Conditioned place preference; Susceptibility; Dopamine D2 receptor; Dopamine transporter