Food deprivation facilitates reinstatement of morphine-induced conditioned place preference: Role of intra-accumbal dopamine D2-like receptors in associating reinstatement of morphine CPP with stress.

The high rate of relapse to drug use is one of the main problems in the treatment of addiction. Stress plays the essential role in drug abuse and relapse; nevertheless, little is known about the mechanisms underlying stress and relapse. Accordingly, the effects of intra-accumbal administration of Sulpiride, as a dopamine D2-like receptor antagonist, on an ineffective morphine dose + food deprivation(FD)- and morphine priming-induced reinstatement of conditioned place preference (CPP). About 104 adult male albino Wistar rats weighing 200-280 g were bilaterally implanted by cannula into the nucleus accumbens (NAc). Subcutaneous (sc) injection of morphine (5 mg kg ) was used daily during a 3-day conditioning phase. After a 24-hr "off" period following achievement of extinction criterion, rats were tested for FD- and priming-induced reinstatement of morphine CPP by an ineffective (0.5 mg kg , sc) and priming (1 mg kg , sc) dose of morphine, respectively. In the next experiments, animals received different doses of intra-accumbal Sulpiride (0.25, 1, and 4 µg/0.5 µL saline) bilaterally and were subsequently tested for morphine reinstatement. Our findings indicated that the 24-hr FD facilitated reinstatement of morphine CPP. Furthermore, the D2-like receptor antagonist attenuated the ineffective morphine dose+ FD- and priming-induced reinstatement of morphine CPP dose-dependently. Also, contribution of D2-like receptors in mediation of the ineffective morphine dose+ FD-induced reinstatement of CPP was greater than morphine priming-induced reinstatement of CPP. The role of dopaminergic system in morphine reinstatement through a neural pathway in the NAc provides the evidence that D2-like receptor antagonist can be useful therapeutic targets for reinstatement of morphine CPP.