Pharmacologically-induced decreases in dopamine activity also yield mixed results in delay discounting behavior. Antagonism of both D1 and D2 receptors increases discounting of delayed rewards in some studies, while having no effect in others.210–212 Similarly, increasing dopamine levels via L-DOPA administration has been shown to increase delay discounting; however amphetamine and dopamine reuptake inhibitors, can either decrease or have no effect on delay discounting in rodents and humans, respectively.212–215 Inconsistent relationships between dopamine and delay discounting may be due to individual differences in baseline dopaminergic signaling,216 as differences in baseline availability of dopamine autoreceptors in the substantia nigra/ventral tegmental area predict increased discounting.217 Consistent with its effects on multiple forms of action inhibition, the noradrenaline reuptake inhibitor atomoxetine reduces choice for small immediate rewards in rats.165
