Dopamine Modulates Effort-Based Decision Making in Rats

Previous research has implicated dopamine as a modulating factor in choice behavior based on effort. The purpose of the present study was to determine the individual contribution of different dopamine receptors to effort-based decision making in rats. Rats were trained in a T-maze to choose a large-reward arm that contained 8 pellets of food over a small-reward arm that contained 2 pellets of food. The rats then were trained to climb progressively higher barriers to obtain the food from the large-reward arm. Using a discounting procedure on each test day, it was found that rats were more likely to choose the small-reward arm after treatment with the D ₁ antagonist, SCH-23390, or the D ₂ antagonist, haloperidol. The dopamine agonist, D-amphetamine, biased the rats toward choosing the large-reward arm and blunted the effects of SCH-23390 or haloperidol. Treatment with the D ₃ receptor antagonist, U99194, or the D ₃ receptor agonist, 7-OH-DPAT, did not alter choice behavior. These data indicate that D ₁ and D ₂ receptors are required for decisions based on effort.