Science and Medicine

Temperature Rhythms Keep Body Clocks in Sync



“Small changes in body temperature can send a powerful signal to the clocks in our bodies,” said Dr. Takahashi.

DALLAS—Researchers at UT Southwestern Medical Center have found that fluctuations in internal body temperature regulate the body’s circadian rhythm, the 24-hour cycle that controls metabolism, sleep and other bodily functions.

A light-sensitive portion of the brain called the suprachiasmatic nucleus (SCN) remains the body’s “master clock” that coordinates the daily cycle, but it does so indirectly, according to a study published by UT Southwestern researchers in the Oct. 15 issue of Science.

The SCN responds to light entering the eye, and so is sensitive to cycles of day and night. While light may be the trigger, the UT Southwestern researchers determined that the SCN transforms that information into neural signals that set the body’s temperature. These cyclic fluctuations in temperature then set the timing of cells, and ultimately tissues and organs, to be active or inactive, the study showed.

Scientists have long known that body temperature fluctuates in warm-blooded animals throughout the day on a 24-hour, or circadian rhythm, but the new study shows that temperature actually controls body cycles, said Dr. Joseph Takahashi, chairman of neuroscience at UT Southwestern and senior author of the study.

Read more: Temperature Rhythms Keep Body Clocks in Sync

 

Too Much Light at Night May Lead to Obesity, Study Finds



“Although there were no differences in activity levels or daily consumption of food, the mice that lived with light at night were getting fatter than the others,” said Laura Fonken.

COLUMBUS, Ohio—Persistent exposure to light at night may lead to weight gain, even without changing physical activity or eating more food, according to new research in mice.

Researchers found that mice exposed to a relatively dim light at night over eight weeks had a body mass gain that was about 50 percent more than other mice that lived in a standard light-dark cycle.

“Although there were no differences in activity levels or daily consumption of food, the mice that lived with light at night were getting fatter than the others,” said Laura Fonken, lead author of the study and a doctoral student in neuroscience at Ohio State University.

The study appears this week in the online early edition of the Proceedings of the National Academy of Sciences.

If the mice are not less active or eating more, what’s causing the bigger weight gain? Results suggest that mice living with light at night eat at times they normally wouldn’t.

In one study, mice exposed to light at night—but that had food availability restricted to normal eating times—gained no more weight than did mice in a normal light-dark cycle.

“Something about light at night was making the mice in our study want to eat at the wrong times to properly metabolize their food,” said Randy Nelson, co-author of the study and professor of neuroscience and psychology at Ohio State.

If these results are confirmed in humans, it would suggest that late-night eating might be a particular risk factor for obesity, Nelson said.

Read more: Too Much Light at Night May Lead to Obesity, Study Finds

   

Greatest Warming in the North, but the Biggest Impact on Life in the Tropics



New research finds that even though the temperature increase has been smaller in the tropics, the impact of warming on life could be much greater there than in colder climates. (Credit: iStockphoto/Jan Rysavy)

In recent decades documented biological changes in the far Northern Hemisphere have been attributed to global warming, changes from species extinctions to shifting geographic ranges. Such changes were expected because warming has been fastest in the northern temperate zone and the Arctic.

But new research published in the Oct. 7 edition of Nature adds to growing evidence that, even though the temperature increase has been smaller in the tropics, the impact of warming on life could be much greater there than in colder climates.

The study focused on ectothermic or cold-blooded organisms (those whose body temperature approximates the temperature of their surroundings). Researchers used nearly 500 million temperature readings from more than 3,000 stations around the world to chart temperature increases from 1961 through 2009, then examined the effect of those increases on metabolism.

“The expectation was that physiological changes would also be greatest in the north temperate-Arctic region, but when we ran the numbers that expectation was flipped on its head,” said lead author Michael Dillon, an assistant professor of zoology and physiology at the University of Wyoming.

Metabolic changes are key to understanding some major impacts of climate warming because a higher metabolic rate requires more food and more oxygen, said co-author Raymond Huey, a University of Washington biology professor. If, for example, an organism has to spend more time eating or conserving energy, it might have less time and energy for reproduction.

“Metabolic rate tells you how fast the animal is living and thus its intensity of life,” Huey said.

Read more: Greatest Warming in the North, but the Biggest Impact on Life in the Tropics

   

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