Washington: Dopamine, or the feel-good brain chemical, has been linked to everything from laziness to creativity and from impulsivity to drug addiction.
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, the receptor numbers were high at night and lower during the day.
The researchers therefore thought this protein may be important in the circadian rhythm, your body`s daily cycle of proteins that regulate daily patterns of feeding, sleeping, body temperature and other functions, LiveScience reported.
During the night, they found, the pineal gland produces a hormone called melatonin that makes you sleepy.
By studying human cells and rat pineal glands in the lab, the researchers have now found that the dopamine D4 receptor hooks up on the outside of pineal gland cells alongside norepinephrine receptors to dampen this melatonin-secretion signal in the early morning.
And while the norepinephrine complex turns up melatonin, along with your sleepiness, when dopamine and its receptor come into the picture, it forms a complex of proteins that does the opposite, said the researchers who detailed their study in the journal PLoS Biology.
When dopamine interacts with its receptor on the outside of the pineal cells, it interferes with the signal sent into the cell, leading to low production and release of melatonin.
Luckily, dopamine`s light-dark cycle means the two (dopamine receptor and the norepinephrine`s receptor, called the andrenergic receptor only hook up at the end of the night.
"The system is expressed in the evening. The dopamine receptor level peaks and you get this nice inhibition of the adrenergic receptor," study researcher Peter McCormick said.
"Everything is sort of on a delay so that by morning time or sunrise you get a complete inhibition of melatonin production."
Studying how these two receptors work together in more depth could give researchers a better understanding of circadian rhythm and its associated disorders, like jet lag, the researchers noted.
It could also be relevant to sleep and mood disorders, such as depression, which involves not only odd dopamine levels in the brain, but also disturbed sleep patterns, they added.