The Effect of D2 Receptor Agonist injection in the Nucleus Accumbens on Restoration of Morphine induced Amnesia by Nicotine in Male Rats

Studies have revealed the effect of morphine and nicotine on different types of memory and learning. These drugs produce more of their effects via the mesolimbic dopaminergic pathway. The aim of the present study was to investigate the effects of intra nucleus accumbens (intra-NAc) injection of the dopamine D2 receptor antagonist (sulpirid) in nicotine’s effect on morphine-induced amnesia. This experimental study was performed on 185 male rats. Rats were anesthetized with intra-peritoneal injection of ketamine hydrochloride، plus xylazine and then placed in a stereotaxic apparatus. Two stainless-steel cannuale were placed in the nucleus accumbens shell. The behavioral testing was started in inhibitory avoidance task، and the step-through latency for entering into the dark compartment was measured for the assessment of memory retention. The amnesia induced by post-training morphine restores with pre-test injection of morphine، nicotine or nicotine plus ineffective dose of morphine. In contrast، pre-test intra-NAc injection of the dopamine D2 receptor antagonist (sulpiride) which had no effect on memory alone prevented the nicotine reversal effect on morphine memory impairment. These results suggest that the dopamine D2 receptor of the nucleus accumbens may play an important role in the improving effect of nicotine on the morphine-induced amnesia.