The GABA(B) receptor agonist baclofen attenuates cocaine- and heroin-seeking behavior by rats

Conditioned stimuli paired with drugs of abuse can acquire motivational properties, and are capable of inducing drug-seeking behavior and relapse to cocaine use. Converging evidence implicates the mesolimbic dopamine (DA) system, through interactions with limbic afferents to the nucleus accumbens, in behavior controlled by conditioned stimuli. The GABA(B) receptor agonist baclofen has been shown to decrease break points in rats responding for cocaine under progressive ratio schedules and also to attenuate activation of limbic cortical areas in human cocaine addicts. The purpose of the present study was therefore to investigate the effects of baclofen on drug-associated cue-controlled cocaine- or heroin-seeking behavior by rats. Under the second-order schedule of reinforcement used in the present study, cocaine or heroin were available after a fixed time interval, while high rates of responding during the interdrug intervals were maintained by the response-contingent presentations of drug-associated conditioned reinforcers. Baclofen decreased stimulus-maintained responding for either heroin or cocaine, but decreased only cocaine intake under an FR1 schedule. These results therefore support preliminary clinical findings and suggest that drugs with GABA(B) receptor agonist properties may aid abstinence in human drug addicts by decreasing the propensity to cue-induced drug-seeking and relapse.