Melatonin decreases cocaine-induced locomotor sensitization and cocaine-conditioned place preference in rats.

Melatonin is a hormone that produces behavioral, pharmacological, and physiological effects through the activation of MT1 and MT2 melatonin receptors. Melatonin receptors participate in the modulation of the reinforcing effects of cocaine. Some studies report that dosing of melatonin decreases cocaine-induced locomotor activity and cocaine self-administration and that luzindole, an MT1, and MT2 melatonin receptor antagonist, blocks the melatonin-dependent decrease in cocaine-induced locomotor activity. The objective of this study was to evaluate the effect of acute or chronic dosing of melatonin on the induction and expression of cocaine-induced locomotor sensitization and cocaine-CPP in rats. Male Wistar rats received cocaine during the induction and expression of locomotor sensitization. Melatonin was administered 30 min before cocaine. After each treatment, locomotor activity was recorded for 30 min. Additionally, dopamine levels were determined in the ventral striatum, the prefrontal cortex (PFc), and the ventral tegmental area (VTA) by HPLC in animals treated with melatonin and cocaine. Melatonin decreased cocaine-induced locomotor sensitization and intracellular dopamine levels, as well as cocaine-CPP. Luzindole blocked the melatonin-induced decrease in the expression of locomotor sensitization in rats. These data suggest that melatonin may be a useful therapeutic agent to reduce cocaine abuse; additionally, they suggest that MT1 and MT2 receptors could be therapeutic targets, useful for the treatment of drug abuse disorder.