Whether exercise may increase dopamine receptors in healthy individuals
Surprisingly, studies have shown that even 8 weeks of exercise increases dopamine D2/D3 receptor activity in methamphetamine users. Similarly, intensive treadmill exercise for 6 weeks increased D2 receptors in mouse models of Parkinson’s Disease (PD), and in human Parkinson’s patients. Additionally, D1 receptor numbers increased following 6 weeks of treadmill exercise in rats.
Moreover, 6 months of endurance training increased the affinity and density of dopamine (DA) receptors.
However, smaller durations of exercise, such as 30 minutes, showed no significant increase in DA receptors. This means that exercise can increase dopamine receptors - if performed somewhat in the long term (perhaps 6 weeks, at least).
In conclusion: numerous studies (I have not cited them all here) have consistently shown that exercise increases dopamine receptor levels. Notably, I have not found research performed specifically on healthy patients - and justifiably so, because limited research funding would rather be allocated to studying how Dopamine receptor function can be restored in disease models as opposed to increasing it in healthy individuals.
Nevertheless, although most of the research focuses on dopamine-deficient conditions such as drug addiction or PD, this would suggest that for healthy humans, Dopamine receptors would also increase and correspond to enhanced feelings of motivation and pleasure.
Neurocognitively, I’m not surprised. Exercise is known to release endorphins, responsible for pleasurable feelings in the brain. Perhaps, plausibly, this pleasure is partly a result of increased dopamine sensitivity via more dopamine receptors. With regards to face validity, I definitely feel more motivated and rewarded when doing more exercise. Really fascinating to think of!