Choosing voluntary exercise over sucrose consumption depends upon dopamine transmission: effects of haloperidol in wild type and adenosine A2AKO mice

Rationale Mesolimbic dopamine (DA) regulates behavioral activation and effort-related decision-making in motivated behaviors. Mesolimbic DA D-2 receptors are co-localized with adenosine A2A receptors, and they interact in an antagonistic manner. Objectives A T-maze task was developed to assess dopaminergic involvement in preference between a reinforcer that involves vigorous voluntary activity (running wheel) and a reinforcer that requires minimal behavioral activation (sucrose pellets). Haloperidol (D-2 antagonist) was administered to adenosine A(2A) receptor knockout (A(2A)KO) and wild-type (WT) littermate controls to assess the involvement of these two receptors in the selection of running wheel activity versus sucrose consumption. Results Under control conditions, mice spent more time running and less time eating. In WT mice, haloperidol reduced time running but actually increased time-consuming sucrose. However, A(2A)KO mice did not show the haloperidol-induced shift from running wheel activity to sucrose intake. Prefeeding reduced sucrose consumption in the T-maze in both strains, indicating that this paradigm is sensitive to motivational devaluation. Haloperidol increased c-Fos immunoreactivity in anterior cingulate cortex (ACg) and nucleus accumbens (Acb) core of WT but not KO mice. Conclusions These results indicate that after DA antagonism, the preference for vigorous physical activity is reduced, while palatable food selection increases. Adenosine A(2A) receptor deletion provides resistance to these effects of D-2 receptor antagonism. These two receptors in Acb core and ACg seem to be involved in the regulation of the intrinsic reinforcing characteristics of voluntary exercise but not in the regulation of the primary reinforcing characteristics of palatable sedentary reinforcers.