Intra-VTA baclofen attenuates cocaine self-administration on a progressive ratio schedule of reinforcement.

The effect of microinjections of baclofen into the ventral tegmental area (VTA), nucleus accumbens, or striatum on cocaine self-administration reinforced on a progressive ratio schedule was investigated. Intra-VTA baclofen produced the most potent modulation of cocaine intake, causing a significant reduction in cocaine-reinforced break points at a dose (56 ng/side) that was substantially lower than doses necessary to produce comparable reductions in the nucleus accumbens or striatum. During the time that cocaine-reinforced responding was suppressed, rats demonstrated the capacity to complete several hundred responses on a concurrently available food-reinforced lever, indicating that the effect of baclofen on cocaine intake was not due to a generalized disruption in operant responding. The results indicate that GABA(B) receptors in the VTA may have the potential to modulate reward processes associated with cocaine use.