Now, a new study has added sleep regulation to that list.
Researchers at the University of Barcelona in Spain found that when dopamine latches onto its receptor in a special part of the brain, it seems to signal the body to "wake up" by turning down levels of the sleepiness hormone melatonin.
The first clue to this new discovery came when researchers noticed that dopamine receptor four, a protein on the outside of certain cells that binds to dopamine, was active in the part of the brain called pineal gland which regulates our internal clock, or the circadian rhythm, by releasing melatonin in response to light.
Interestingly, presence of the dopamine receptor on pineal gland cells seemed to cycle with the time of the day
