Behavioral sensitization to WIN55212.2 in rats pretreated with heroin.

There is evidence of similarities and interactions between central opioid and cannabinoid system with reference to drug reinforcement and abuse. Here we demonstrate that repeated injection of heroin produces behavioral sensitization towards administration of the synthetic cannabinoid receptor agonist WIN55212.2 in the rat. These effects were blocked by both the cannabinoid antagonist SR141716A and the opioid antagonist naloxone. These findings suggest that repeated exposure to heroin produces neuroadaptative changes in brain circuits that contribute to mediate the behavioral consequences of acute administration of WIN55212.2. The present results expand our knowledge on the interactions between central opioid and cannabinoid systems with respect to drug abuse.