A New Cure for Jet Lag?

Study in animals suggests temperature shift in brain can reset body clock

(HealthDay is the new name for HealthScoutNews.)

TUESDAY, July 22, 2003 (HealthDayNews) -- Synchronizing the body's biological clock to a new time zone might someday just require changing the temperature of your brain.

That could be the long-term application of research in which scientists reset the biological clocks of laboratory rats by changing the temperature of their brain. But they caution that much more work needs to be done to see if the same might apply to time-zone-hopping human travelers. The study appears in the August issue of the Journal of Neurophysiology.

Biological clocks drive circadian rhythms and are present in almost every living organism, says study author Erik Herzog, an assistant professor of biology at Washington University in St. Louis.

"Light acts indirectly through the eyes to synchronize your clock to local time," he says. In his new research, he found that brain temperature acts directly on the clock.

The biological clocks drive the 24-hour cycles of alertness and affect hormone levels. And the so-called control panel for these operations is what is termed "the brain's Timex" -- the suprachiasmatic nucleus (SCN), neurons located in the hypothalamus. The hypothalamus is an area in the brain that produces "controlling" hormones which, in turn, regulate metabolism and other processes.

"We wanted to see if we could take control of the biological clock in a dish," Herzog says.

So Herzog took the SCN out of laboratory rats, put each in a dish, and exposed it to different temperatures. They shifted the temperature to mimic the differences that normally occur from day to night.

Rats are nocturnal animals, with body temperature normally rising at night. So Herzog reversed the normal temperatures, warming the SCN during the day and cooling it at night and successfully reversed the normal daily temperature fluctuations, resetting the clock.

"It's the first time anyone has trained the clock in a [laboratory] dish," he says.

Herzog also tested whether the SCN could be resynchronized just by exposing it to light. This idea was put forth about five years ago, when some research suggested photoreceptors that help reset the body clock might be located elsewhere in the body besides the eyes, including the SCN. Some experts even suggested shining light on the backs of the knees to help shift the body clock to a new time zone.

But when Herzog exposed the SCN to light at night and dark during the day, no resynchronization occurred.

"Light doesn't synchronize the clock directly," he concludes. "Light through the eyes can." And Herzog says light and temperature might work synergistically to reset the clock.

"It's an interesting finding, but the next step should be to repeat the study in day-active animals," says Dr. Alfred Lewy, director of the Sleep and Mood Disorders Laboratory at Oregon Health and Science University. "Rats' temperatures are high at night and low during the day," says Lewy, a pioneer in the field who has studied melatonin, bright light and other treatments for jet lag. "Humans are opposite."

Herzog acknowledges that studying day-active animals is a necessary part of future research. "It is something we need to look at," Herzog says.

"It's too soon to say this has any practical applications," Lewy adds.

More information

Learn about the hypothalamus from the National Library of Medicine. For information on jet lag, go to the National Sleep Foundation.

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