For Immediate Release
March 28, 2000
Contact: Alisa Giardinelli
(610) 690-5717
[email protected]
http://www.swarthmore.edu/Home/News
Swarthmore Biologist Sheds New Light on Seasonal Biological Clock
How do mammals know when to migrate, reproduce, or take other action necessary for their survival? According to a new study by a Swarthmore College biologist, a gland in the brain helps maintain the body's synchronization with the environment.
Associate Professor of Biology Sara Hiebert studies the circannual rhythms, or annual cycles, of animals with a "seasonal life." Although it is known that circannual and circadian, or daily, rhythms provide an important basis for the control of many seasonal activities, the exact nature of the internal mechanism, or "biological clock," that controls circannual rhythms has been a mystery.
In a three-year-long experiment with ground squirrels, the results of which appear in the April issue of the Journal of Biological Rhythms, Hiebert and her colleagues at the University of California at Berkeley found that the brain's pineal gland is essential for the synchronization of the squirrel's annual rhythms with the solar year. Previous studies showed the pineal gland registers light and secretes the hormone melatonin in response to darkness. Hiebert determined that without melatonin from this gland, the squirrels were not able to reproduce or accumulate body mass in 12-month cycles.
Although she is reluctant to draw any direct correlation to humans, Hiebert says it is conceivable to think that knowing about the daily and seasonal basis of biological rhythms could help scientists to design treatments that relieve some of the symptoms of seasonal disorders. "Do humans have annual rhythms?" she asks. "One hypothesis is that circannual rhythms are related to seasonal affective disorder (SAD). Animal studies can provide important background information for designing human experiments."
According to Hiebert, circannual rhythms appear to be more common in animals that hibernate, but in general are much less widespread than circadian rhythms and are therefore not as widely understood. Her study addresses one of the two main issues surrounding these rhythms -- what synchronizes the circannual clock with the environment.
Hiebert also studies the role of stress hormones in regulating torpor, a state similar to hibernation but much shorter in duration, in hummingbirds. Her work examines stress and how it regulates the hummingbird's energy economy.
Located near Philadelphia, Swarthmore is a highly selective liberal arts college with an enrollment of 1,400. Swarthmore is ranked the number one liberal arts college in the country by U.S. News & World Report.
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