Taking a dopamine agonist (something like Pramipexole, i know it can be prescribed for bipolar and unipolar depression, just not sure how easy it is to get prescribed) can cause the down regulation of dopamine receptors and maybe taking something like a dopamine reuptake inhibitor would help with anhedonia. There's also a few natural supplements and foods that increase dopamine production, and I think there are some natural over the counter dopamine agonist. Regardless of this, the down regulation of dopamine receptors ought to happen naturally as well, over a period of time.