Cannabidiol modulates the METH-induced conditioned place preference through D2-like dopamine receptors in the hippocampal CA1 region

The main problem with addiction is a relapse with a high rate in methamphetamine (METH) abusers. Using addictive drugs repetitively will cause the reward. METH reward is due to an increase in dopamine levels, and the endocannabinoid system (ECS) has a modulatory role in reward through CB1 receptors. On the other hand, the hippocampus plays an important role in learning and memory, so it is involved in the neuroplasticity caused by METH abuse. Cannabidiol (CBD) has been shown to reduce the effects of METH through different mechanisms such as increasing the ECS activity, regulating emotional memory in the ventral hippocampus through D2-like dopamine receptors, and decreasing the mesolimbic dopaminergic activity. The present study tried to find out the role of hippocampal CA1 D2-like dopamine receptors (D2R) in the effects of cannabidiol on the acquisition and expression of METH-induced conditioned place preference (METH-CPP) in rats by using microinjection of sulpiride as a D2R antagonist. For this purpose, different groups of animals received different doses of sulpiride (0.25, 1, and 4 μg/0.5 μL DMSO; CA1), once prior to the injection of CBD (10 μg/5 μL for acquisition and 50 μg/5 μL for expression; ICV) and once in the absence of CBD. Control groups were also considered. In brief, findings showed that cannabidiol decreases METH-induced CPP. Intra-CA1 administration of sulpiride reversed the decreasing effects of cannabidiol on METH-induced CPP in both acquisition and expression phases but more prominent in the expression phase. The results showed that sulpiride did not affect the METH-induced CPP in the absence of cannabidiol. In conclusion, this study demonstrated that cannabidiol decreased METH-induced CPP in part through interaction with hippocampal CA1 D2-dopamine receptors.