Comments: Two studies that show that aerobic exercise increases in dopamine (D2) receptors. D2 receptors decrease with addictions, and are a major cause of desensitization. This study shows that long-term endurance training can increase dopamine D2 receptors in the reward circuitry (striatum).

Endurance training effects on striatal D2 dopamine receptor binding and striatal dopamine metabolite levels (1987)
Neurosci Lett. 1987 Aug 18;79(1-2):138-44.
MacRae PG, Spirduso WW, Cartee GD, Farrar RP, Wilcox RE.

Source