Peripheral electrical stimulation-induced suppression of morphine-induced CCP in rats: a role for dopamine in the nucleus accumbens.

In the previous study we reported that morphine-induced conditioned place preference (CPP) could be suppressed by peripheral electric stimulation (PES), an effect related to the increased gene expression of opioid peptides in the central nervous system. Considering that opioids were known to elevate dopamine (DA) activity in the mesolimbic brain, the present study was designed to further analyze the possible involvement of the mesolimbic dopaminergic system (MLDS) in the suppressive effect of PES on the rewarding effects of morphine in SD male rats. We found that morphine-induced CPP can be successfully suppressed by PES, an effect accompanied by a reversal of the increased tissue contents of DA and its metabolites in the nucleus accumbens (NAc) of morphine-induced CPP rats. Our results suggest that MLDS seems to play important roles in the mechanisms underlying PES's suppression of the rewarding effect of drug-associated environmental cues in the rat.