The role of dopamine in overcoming aversion with exercise.

Exercise increases positive mood and the ability to buffer the impact of aversive events on the brain and behavior, but if and how these beneficial effects of exercise interact to confer an ability to overcome aversion is unknown. Exercise is a natural reward that produces unique adaptations in mesolimbic and nigrostriatal dopamine circuits involved in motor activity and reward. The current review summarizes exercise adaptations in dopaminergic circuits that lead to a hyperdopaminergic state; during which dopamine release in the striatum is sensitized during exposure to non-exercise stimuli, even aversive stressors that do not typically activate reward-related dopamine circuits. Sensitized dopamine release in the striatum of physically active organisms shifts recruitment of striatal medium spiny neurons during aversive events from those expressing dopamine 2 (D2) receptors implicated in aversion and stress vulnerability, towards those expressing dopamine 1 (D1) receptors implicated in reward and stress resilience. Neural circuits through which a hyperdopaminergic state and subsequent activity of D1-expressing neurons in the striatum could interact with stress circuits previously implicated in exercise-induced stress resistance are outlined. The data summarized provide a novel neural circuit perspective for how dopaminergic mechanisms involved in movement and emotion regulation could overlap with those critical for the ability of exercise to overcome aversion.