The experiment was designed to investigate the variation of DAT and D2 receptor in morphine administered and 1

2

3 day abstinent rats. Morphine exposure was induced by repeated morphine (i.p.) treatment for 8 days. Conditioned place preference test was conducted to evaluate the drug seeking behaviour and morphine dependence of rats with morphine exposure. Biodistribution of the imaging agents 125I-β-CIT and 125I-IBZM was used to evaluate the central DAT and D2 receptor during morphine exposure and 1

2

3 day’s abstinence. Results reveal the following facts. (1) The morphine abstinent rats showed diarrhea and body-shake 1 day after morphine withdrawal. (2) For morphine group

125I-β-CIT %ID/g in ST and NAC was higher than that of the 1

2

3 day’s abstinent rats and control (P<0.05). No difference was found between 1

2

3 day’s abstinent group and control group (P>0.05). (3) 125I-IBZM %ID/g in ST

NAC and HIP in morphine rats were lower than those of the abstinent and control rats (P<0.05). The 125I-IBZM %ID/g in ST and NAC gradually increased with the abstinent days. While in ST the %ID/g among the abstinent rats was all lower than that of the control rats

in NAC the %ID/g was still lower in 1 day’s abstinent rats (P<0.05)

and no difference in 2 and 3 day’s abstinent rats was observed in comparison with the control (P>0.05)

indicating the reduction of hyper-activated DAT and the increase of down-regulatory D2 receptor induced by morphine during morphine withdrawal. Our results confirmed that the dopamine system

especially DAT and D2 receptor in mesolimbic and meso-striatum pathway

has been implicated in morphine treatment. The rewarding properties of morphine and the somatic expression of morphine abstinence were related to changes in mesolimbic and meso-striatum dopaminergic activity.