Chronic alcohol consumption blunts the biological clock’s ability to synchronize daily activities to light, disrupts natural activity patterns and continues to affect the body’s clock (circadian rhythm), even days after the drinking ends, according to a new study with hamsters.
The study describes the changes that drinking can produce on the body’s master clock and how it affects behavior. The research provides a way to study human alcoholism using an animal model, said researcher Christina L. Ruby.
The study appears in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. Christina L. Ruby, Allison J. Brager, Marc A. DePaul, and J. David Glass, all of Kent State University, and Rebecca A. Prosser of the University of Tennessee, conducted the study. The American Physiological Society published the research.
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Alcohol consumption affects the master clock, located in the suprachiasmatic nucleus (SCN) section of the brain. This clock controls the circadian cycle, a roughly 24-hour cycle, which regulates sleeping and waking, as well as the timing of a variety of other physiological functions, such as hormonal secretions, appetite, digestion, activity levels and body temperature. The SCN synchronizes physiological functions so that they occur at the proper times and keeps these functions synchronized with daylight. Disruption of the clock dramatically increases the risks of developing cancer, heart disease, and depression, among other health problems.
The researchers used hamsters to find out how alcohol affects circadian rhythms. Although hamsters are nocturnal, light synchronizes their clocks, just as with humans. The animals were divided into three groups, differing only on what they drank. The control group received water only. A second group received water containing 10% alcohol and the third group received water containing 20% alcohol. Hamsters, when given a choice, prefer alcohol, which they metabolize quickly.
The animals drank as much as they wanted and lived in an environment that provided 14 hours of light and 10 hours of darkness each day.
The researchers recorded the activity levels of the three groups throughout the day. Late in the dark cycle, about three hours before the nocturnal animals would normally be settling in to sleep, the researchers put on a low-level light for 30 minutes. The light was similar to the dim light of dawn. At another time, the groups received a brighter light, akin to the light in an office building. Hamsters exposed to the light late in their active cycle will normally settle down to sleep at the same time, but will wake up earlier. In effect, the light pushes their circadian clock forward.
In addition, the researchers tracked how long it takes alcohol to travel to the master clock in the brain. They also took regular readings of subcutaneous alcohol levels, which are akin to blood alcohol levels. In the final phase of the experiment, the hamsters that received alcohol were switched to regular water to examine the effects of withdrawal.
The study found that:
The researchers aim to apply the research to people, who also show circadian disruptions from drinking. Specifically, the study suggests the following:
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