New research led by a University of Washington biologist demonstrates that there are at least two circadian clocks in the mammal brain, one that sticks strictly to an internal schedule and another that can be altered by external influences such as light and dark.

Typically the two clocks are synchronized so that various physical functions are in tune with each other, said Horacio de la Iglesia, a UW assistant professor of biology. But make a long plane trip or switch your 8-to-5 work schedule to begin at midnight and things can get out of kilter.

"When you travel to Europe, the rest-activity cycle will adjust relatively quickly. In two or three days you'll probably be sleeping when it's dark," de la Iglesia said. "But your temperature or hormone-release cycles might still be on Seattle time, affecting for instance how well you sleep."

A bit of brain tissue called the suprachiasmatic nucleus, a daily pacemaker that regulates rhythms such as sleep and wakefulness, has thousands of cells called neurons with synchronized circadian activities. But the neurons in the nucleus can be grouped into at least two secondary clocks that can become disconnected from one another when exposed to artificial day-night cycles.

For the study, a group of rats was exposed to artificially created 22-hour days, with 11 hours each of light and dark. With the shortened 22-hour days, the researchers found that what normally is daytime activity began to expand into the artificial night hours, and that enabled them to look at the interplay of two genes in the rats' brain clocks. One gene, called Per1, is active during the day and the other, Bmal1, is active at night.

The scientists found that when a rat behaved as expected, its suprachiasmatic nucleus contained Per1 during light periods and Bmal1 during dark. But when the daytime behavior
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Contact: Vince Stricherz
vinces@u.washington.edu
206-543-2580
University of Washington
12-May-2004