The antidepressant-like effects of zinc (Zn) have been documented in some animal models of depression. In addition, antidepressants may reduce the abuse potential of opioids by affecting their rewarding effect. Hence, this study was performed to investigate the effect of Zn on the expression of morphine-induced conditioned place preference (CPP) in male rats. We used an unbiased CPP paradigm for investigating the effect of Zn. The intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administrations of Zn (5-20 mg/kg, i.p., and 10 nmol/rat, respectively) with or without morphine did not induce conditioned place aversion (CPA) or CPP during acquisition phase. However, the same i.p. and i.c.v. administrations of Zn induced morphine-like CPP in the expression phase. Pre-treatment with dopamine receptor antagonists (SCH23390, sulpiride, and haloperidol) and serotonin receptor antagonists (WAY100135, ketanserin, and ondansetron) reversed the enhancement effect of Zn on the expression of morphine-induced CPP (especially 20mg/kg, i.p. and 10 nmol/rat, i.c.v.). These findings suggest that acute i.p. and i.c.v administration of Zn might enhance the rewarding properties of morphine through involvement with dopaminergic and serotonergic neuronal systems.
Keywords: Conditioned place preference; Expression; Morphine; Rat; Reward; Zinc sulfate.