Role of muscles accumbens dopamine D1 and D2 receptors in instrumental and Pavlovian paradigms of conditioned reward.

RATIONALE: This study investigated the role of nucleus accumbens dopamine D1 and D2 receptors in two different paradigms of conditioned reward.
OBJECTIVE: We addressed the question whether accumbal dopamine is important for the motor or for the motivational components of reward.
METHODS: We compared the effects of intra-accumbal infusion of the dopamine D1 receptor antagonist SCH23390 (0.3, 1.0, 3.0 microg) and the D2 receptor antagonist sulpiride (0.3, 1.0, 3.0 microg) on conditioned lever pressing for food, with the effects on the inhibition of the startle response by a conditioned reward signal.
RESULTS: Both the D1 and the D2 antagonist dose-dependently attenuated conditioned lever pressing for reward under a fixed-ratio of responding and increased the consumption of freely available lab chow. However, the preference for freely available pellets, and the attenuation of the startle response in the presence of a conditioned stimulus predicting reward were not impaired by blockade of accumbal dopamine receptors.
CONCLUSIONS: Our data support the idea that dopamine in the nucleus accumbens is necessary for instrumental response selection in the context of reward rather than for the mere motor performance of behavior or for the evaluation of the hedonic properties of rewarding stimuli.