Blockade of dopamine D₁ receptors, but not D₂ receptors, decreases motivation in a novel effort-discounting paradigm in common marmosets.

Effort-based decision-making paradigms have recently been used to measure motivation in healthy subjects and patients with neuropsychiatric disorders. In the present study, we developed a novel effort-discounting paradigm using a touch-panel system in common marmosets. Marmosets were trained to choose between a low-reward (a piece of cake) requiring low-effort (one touch response) versus high-reward (three pieces of cake) requiring one of three different effort levels (one, two, or four touch responses). Because the number of trials per session was kept constant, the selection of the high-reward choice was always the optimal strategy to receive the maximum number of rewards. Marmosets' high-reward rates were reduced as the physical effort requirement was increased, when they were tested using effort discounting in either ascending or descending order of effort intensity. It indicates that marmosets' decisions could be attributable to cost-benefit evaluation, but not to their fatigue or satisfaction with the reward during the progression of the paradigm. The high dose of dopamine D₁ receptor antagonist SCH-39166 (0.03 mg/kg) reduced the high-reward choice rate, only when more effort was required to obtain the high-reward than the low-reward. On the other hand, the D₂ receptor antagonist raclopride (0.01 and 0.03 mg/kg) unexpectedly did not affect the high-reward choice rate, but the high dose did increase omission rate. Our finding suggests that dopamine D₁ receptor signaling may play a more important role in effort-based decision making than D₂ receptor signaling in marmosets. Our novel behavioral paradigm would be useful in translational research focused on motivational deficits. (PsycINFO Database Record (c) 2018 APA, all rights reserved).