Glutamate transmission in the nucleus accumbens mediates relapse in cocaine addiction

Elevated dopamine transmission in the nucleus accumbens is thought to be a primary mediator of addiction to cocaine. However, repeated exposure to cocaine is associated with the recruitment of glutamate transmission. This poses the possibility that the behaviors characterizing cocaine addiction, such as craving-induced relapse, may not be preferentially mediated by dopamine transmission. An animal model of relapse was used to demonstrate that glutamate, and not dopamine transmission in the nucleus accumbens, is a primary mediator of cocaine-induced reinstatement of drug-seeking behavior. Reinstatement was produced by a systemic injection of cocaine or by the microinjection of the glutamate receptor agonist AMPA or dopamine into the nucleus accumbens. It was found that microinjection of an AMPA receptor antagonist into the nucleus accumbens blocked reinstatement by all compounds, whereas a dopamine receptor antagonist was effective only in blocking reinstatement by intra-accumbens dopamine administration. These data suggest an important role for nucleus accumbens glutamate and not dopamine transmission in cocaine-induced relapse to drug-seeking behavior.