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MONDAY, APRIL 19, 2004
Contact: Donna Krupa
703.967.2751 (cell)
703.527.7357 (office)
djkrupa1@aol.com
APS Newsroom: April 17-21, 2004
Washington, DC Convention Center
East Registration Area/Flex Unit
Telephone: 202.249.4009
How Do Animals Exposed To 24-Hour Light Retain Their
Wake-Sleep Habits?
New study of free-living animals in
the natural continuous light of the Arctic finds that rodents maintain a
24-hour schedule, vs. the 26-hour schedule observed in control animals kept
in laboratory conditions
Washington, DC – The phrase “biological clock”
has expanded from scientific observation to American slang. When we hear
this phrase, many of us assume it refers to the amount of time left for a
woman to start a family. For the scientist, the biological clock refers to a
process that took millions of years to evolve – the conditioning of plants
and animals by a light cycle that starts with dawn and ends with sunset.
The cycle of dawn and dusk changes with the seasons
everywhere in the world (except at the equator, where there is always 12
hours of daylight and 12 hours of darkness). In order to compensate for the
seasonal variations of light, mammals likely have an adjustable daily
program under the regulation of a biological clock.
But how do mammals in the Arctic – which is
characterized by months of full light followed by months of full darkness
-- retain their sleep and awake habits in such unusual circumstances? After
analyzing the reactions of certain mammals following 82 days of continuous
daylight in the summer and 82 days of continuous darkness in the winter, a
team of researchers may have begun to identify a clue.
A New Study
The research is captured in a presentation entitled,
“Cardiac Physiology of Mammals in Arctic Light Cycle: Heart Rates and
Biological Clocks.” The authors, G. Edgar Folk, Diana L. Thrift, James B.
Martins, and Miriam B. Zimmerman, all from the University of Iowa, Iowa
City, IA, will present their findings at the American Physiological
Society’s
(APS) (www.the-aps.org)
annual scientific conference, Experimental Biology 2004, being held
April 17-21, 2004, at the Washington, D.C. Convention Center.
Methodology and Results
The researchers analyzed the biological clocks using
cardiac physiology. They recorded the mammals’ daily circadian rhythm using
heart rate to show the rhythm of sleep and wakefulness.
Control laboratory rats (N=4) were exposed to
artificial continuous light and demonstrated the Aschoff effect, where the
circadian activity pattern changes quantitatively with the intensity of the
light. This group took on a 26-hour day.
This was not the case when the experiment was repeated
in the field at the Naval Arctic Research Laboratory - with two species of
Arctic rodents exposed to continuous daylight (nocturnal porcupines [Erethizon]
N=4, and hibernators, the Arctic ground squirrel [Spermophilis] N=6).
Under these circumstances, both species had a specific time of sleep and of
wakefulness. In fact, the Arctic rodents, which had undergone 82 days of
continuous sun above the horizon, had a crisp, 24-hour day-night rhythm of
sleep and wakefulness.
Conclusions
The free-living animals in the Arctic had regular
sleep-awake cycles, despite having 82 days of continuous sun. The intriguing
question is whether or not these animals have found a clue in the external
environment to take the place of the missing sunset. The researchers
hypothesize that because the sun during this period is nearer the horizon at
one part of the day, this might act as a clue for the biological clocks.
As the American economy requires its work force to
abandon traditional work hours of “nine to five,” it becomes more important
for us to understand how the body’s biological clock can respond to
unnatural light clues and adapt to a changing environment. This study is
another step in the continuing research towards such comprehension.
- end -
The
American Physiological Society (APS) was founded in 1887 to foster basic and
applied science, much of it relating to human health. The Bethesda, MD-based
Society has more than 11,000 members and publishes 3,800 articles in its 14
peer-reviewed journals every year.
***
Editor’s
Note: For further information or to schedule an interview with a member of
the research team, please contact Donna Krupa at 703.967.2751 (cell),
703.527.7357 (office) or at
djkrupa1@aol.com. Or contact the APS newsroom at 202.249.4009 between
9:00 AM and 6:00 PM EDT April 17-21, 2004.
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