The brain's internal clock continually takes its temperature

March 7, 2018, National Institutes of Health
An increase in 'hotter' colors after cooling indicates more firing in neurons of the circadian clock Credit: Shafer lab, University of Michigan, Ann Arbor

Circuits in the brain act as an internal clock to tell us it is time to sleep and to control how long we then stay asleep. A new study in flies suggests a part of that clock constantly monitors changes in external temperature and integrates that information into the neural network controlling sleep. The study was published in Nature and was supported by the National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institutes of Health.

"This study takes advantage of the powerful model system of the fly's network to demonstrate how temperature cues from the environment are used to control the time and duration of sleep," said Janet He, Ph.D., program director, NINDS.

The circadian clock is a fundamental process found in nearly every living organism that coordinates sleep behavior with changes in the environment. The link between the light/dark cycle and the onset of sleep is well recognized; however, changes in temperature also appear to affect sleep patterns in humans.

"The clock discovered in flies more than 30 years ago is essentially the same one found in the human brain," said Orie Shafer, Ph.D., associate professor at the University of Michigan, Ann Arbor, and senior author of this study. "Circadian clock studies are beautiful examples of how the fly has important things to tell us about how our bodies work."

By using a special fluorescent protein that changes from green to red when neurons fire, Dr. Shafer and his team watched the activity of different parts of the fly brain's circadian clock while they increased or decreased the surrounding temperature. To their surprise, an area in the fly brain's circadian clock called the DN1p increased its activity when cooled and became less active when heated.

"We knew that light excites the circadian clock overall and that light and heat typically increase at the same time, so it was completely unexpected to find a region of the clock that increased its activity in response to cooling," said Dr. Shafer.

As experienced by anyone who has traveled across time zones, the circadian clock can be "reset" over time in response to new day/light cycles. The clock of flies can be retrained to new cycles of either light or temperature, so Dr. Shafer and his colleagues next looked at whether the DN1p is involved in resetting the clock to a new heating/cooling cycle.

Because DN1p neurons are thought to be sleep-promoting, the researchers blocked their activity or eliminated them genetically. Both affected the flies' ability to retrain their sleep cycle in response to changes in temperature, highlighting the importance of the DN1p for the control of sleep behavior.

"Because flies' bodies are translucent, their can respond to light directly," said Dr. Shafer. "We next asked whether temperature worked in the same way or required external organs."

In flies, temperature could be sensed directly by neurons in the brain or via nerve impulses from sensory organs in the body. To distinguish between the two, the investigators genetically manipulated or physically removed the sensory organs and found that the DN1p neurons no longer responded to changes in temperature. This meant that the clock interprets temperature signals from the body rather than sensing temperature changes directly.

The circadian clock of larger animals and humans is also sensitive to changes in temperature, and because of their larger size, would require input from external sensory organs. The fact that, despite its small size, the fly clock also relies on sensors outside the brain suggests that the findings of this study could have broad implications in the control of sleep in humans.

Explore further: Getting sleepy? Fruit flies constantly tune into environmental temperature to time sleep

More information: Swathi Yadlapalli et al, Circadian clock neurons constantly monitor environmental temperature to set sleep timing, Nature (2018). DOI: 10.1038/nature25740

Related Stories

Getting sleepy? Fruit flies constantly tune into environmental temperature to time sleep

February 21, 2018
Humans and fruit flies may have not shared a common ancestor for hundreds of millions of years, but the neurons that govern our circadian clocks are strikingly similar.

Understanding a fly's body temperature may help people sleep better

February 13, 2018
In findings that one day may help people sleep better, scientists have uncovered the first molecular evidence that two anciently conserved proteins in the brains of insects and mammals share a common biological ancestry as ...

The circadian clock is like an orchestra with many conductors

March 27, 2014
You've switched to the night shift and your weight skyrockets, or you wake at 7 a.m. on weekdays but sleep until noon on weekends—a social jet lag that can fog your Saturday and Sunday.

Vibrations influence the circadian clock of a fruit fly

January 31, 2014
The internal circadian clock of a Drosophila (fruit fly) can be synchronised using vibrations, according to research published today in the journal Science. The results suggest that an animal's own movements can influence ...

'Jet-lagged' fruit flies provide clues for body clock synchronisation

January 17, 2013
New research led by a team at Queen Mary, University of London, has found evidence of how daily changes in temperature affect the fruit fly's internal clock.

Protein involved in temperature entrainment of brain for circadian clock in fruit fly identified

November 19, 2015
(Phys.org)—A team of researchers from institutions in the U.K. and Switzerland has identified a protein that is heavily involved in entrainment in fruit fly brains as part of coordinating the circadian clock. In their paper ...

Recommended for you

Japanese team creates human oogonia using human stem cells in artificial mouse ovaries

September 21, 2018
A team of researchers with members from several institutions in Japan has successfully generated human oogonia inside of artificial mouse ovaries using human stem cells. In their paper published in the journal Science, the ...

Researchers explore how changes in diet alter microbiome in artificial intestine

September 21, 2018
Using an artificial intestine they created, researchers have shown that the microbiome can quickly adapt from the bacterial equivalent of a typical western diet to one composed exclusively of dietary fats. That adaptation ...

A new approach to developing a vaccine against vivax malaria

September 21, 2018
A novel study reports an innovative approach for developing a vaccine against Plasmodium vivax, the most prevalent human malaria parasite outside sub-Saharan Africa. The study led by Hernando A. del Portillo and Carmen Fernandez-Becerra, ...

Study identifies stem cell that gives rise to new bone and cartilage in humans

September 20, 2018
A decade-long effort led by Stanford University School of Medicine scientists has been rewarded with the identification of the human skeletal stem cell.

Scientists grow human esophagus in lab

September 20, 2018
Scientists working to bioengineer the entire human gastrointestinal system in a laboratory now report using pluripotent stem cells to grow human esophageal organoids.

Researchers identify human skeletal stem cells

September 20, 2018
Human skeletal stem cells that become bone, cartilage, or stroma cells have been isolated from fetal and adult bones. This is the first time that skeletal stem cells, which had been observed in rodent models, have been identified ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.