Adenosine A2a blockade prevents synergy between [mu]-opiate and cannabinoid CB1 receptors and eliminates heroin-seeking behavior in addicted rats

Relapse is the most serious limitation of effective medical treatment of opiate addiction. Opiate-related behaviors appear to be modulated by cannabinoid CB1 receptors (CB1) through poorly understood cross-talk mechanisms. Opiate and CB1 receptors are coexpressed in the nucleus accumbens (NAc) and dorsal striatum. These regions also have the highest density of adenosine [A.sub.2A] receptors ([A.sub.2A]) in the brain. We have been investigating the postsynaptic signaling mechanisms of/[micro]-opiate receptors (MORs) and CB1 receptors in primary NAc/striatal neurons. In this article, we present evidence that MOR and CB1 act synergistically on cAMP/PKA signaling in NAc/striatal neurons. In addition, we find that synergy requires adenosine and [A.sub.2A]. Importantly, an [A.sub.2A] antagonist administered either directly into the NAc or indirectly by i.p. injection eliminates heroin-induced reinstatement in rats trained to self-administer heroin, a model of human craving and relapse. These findings suggest that [A.sub.2A] antagonists might be effective therapeutic agents in the management of abstinent heroin addicts. PKA | addiction | nucleus accumbens | gene activation