The GABA-B positive modulator GS39783 decreases psychostimulant conditioned-reinforcement and conditioned-reward

Baclofen, a γ-amino-butyric-acid (GABA)(B) receptor agonist, can reduce cue-enhanced cocaine-seeking in rats and attenuate cue-evoked craving in cocaine addicts. However, baclofen also has sedative effects that might interfere with its efficacy in reducing cocaine's rewarding effects. The present study aimed at comparing the effects of baclofen with the GABA(B) -receptor positive allosteric modulator GS39783 on psychostimulant conditioned cues. Two identically trained groups of male Lister-Hooded rats were baselined on a new responding for a light stimulus previously paired with cocaine self-administration. One group was treated with the GABA(B) -receptor positive allosteric modulator GS39783 (0, 10, 30, 100 mg/kg, i.p.), the other with baclofen (0, 0.6, 1.25, 1.9, 2.5 mg/kg, i.p.). In another series of experiments, male Wistar rats received GS39783 (0, 10, 30, 100 mg/kg, i.p.) or baclofen (1.25 mg/kg) prior to the expression of a conditioned place preference (CPP) to amphetamine (2 mg/kg i.p.). Both GS39783 (30 and 100 mg/kg) and baclofen (2.5 mg/kg) significantly decreased responding for the cocaine cue; however, only GS39783 (30 mg/kg) reduced lever pressing responding without interfering with locomotor activity. Both GS39783 (30 and 100 mg/kg) and baclofen (1.25 mg/kg), significantly blocked the expression of amphetamine CPP without affecting locomotor activity. These findings suggest that GABA(B) positive allosteric modulators can modulate discrete and contextual psychostimulant conditioned stimuli in a manner dissociable from unwanted sedative effects and may offer a novel therapeutic approach to treat cravings and relapse to drug-taking triggered by stimuli associated with psychostimulant use.