Penn Sleep Centers Newsletter
 

Winter 2006

Asleep at the Wheel?
Sleep Apnea and Heart Disease
Cognitive-Behavioral Treatment of Insomnia
Do Flies and Worms Sleep?
Advice for Sleepy Students
New Headquarters for Penn Sleep Centers
 
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Do Flies and Worms Sleep?
Penn Researchers Look for an Answer

Can you tell if a fly is asleep? This is precisely the question asked seven years ago by Dr. Joan Hendricks, who is now the Dean of the School of Veterinary Medicine at the University of Pennsylvania. In collaboration with Dr. Amita Sehgal and Dr. Allan Pack of the Penn Center for Sleep and Respiratory Neurobiology (CSRN), Dr. Hendricks wanted to determine if the fruit fly Drosophila melanogaster, an animal used since the early 1900s for genetic studies in biology, has a sleeplike state much as we do. But unlike human studies, where one can measure brain electrical activity to distinguish sleep from the waking state, one cannot easily measure fly brain waves. Instead, Dr. Hendricks used behavioral measures.

It was already known that Drosophila are not active all day, but rather have rest and activity patterns that follow an approximately 24-hour, or circadian, rhythm. They are active during the day and inactive at night, just like us. To determine if the inactive period corresponded to fly sleep, or simply to restful wakefulness, Dr. Hendricks first asked if the flies were less responsive during this period, much as we are less likely to respond to stimuli when asleep. She found that indeed, the flies were less likely to move in response to a gentle tap during these nocturnal quiescent periods than during the day.

In addition, just as we become increasingly sleepy with sleep deprivation and will sleep during the day if awake all night, the flies too fell asleep during a time when they are normally active after staying awake all night. Caffeine, a chemical we consume in soft drinks and coffee to keep us awake, also keeps the fly awake, indicating that the underlying sleep regulatory mechanisms are the same in flies as in humans.

We spend one third of our lives asleep and yet the purpose of sleep remains unknown.

Why does it matter that fruit flies sleep? It means that sleep is so fundamental to animal life that it is likely to be found in all animals. David Raizen, MD, PhD, of the Department of Neurology is a CSRN clinician scientist who is extending the findings in fruit flies to an even simpler animal known as Caenorhabditis elegans, a soildwelling round worm. He has identified a quiescent behavioral state that like sleep in humans and mice is controlled by the activity of circadian genes and that cannot be bypassed, just as sleep cannot be bypassed in humans.

We spend one third of our lives asleep and yet the purpose of sleep remains unknown. If we can understand the purpose of sleep in the lowly fly or worm, perhaps we can gain insight as to why we need sleep. In addition, genes that control sleep can be easily identified and studied in fruit flies and round worms; these genes are likely to also have relevance to human sleep.

If we knew which genes function to control sleep and wakefulness, then we could study how these genes malfunction in human sleep disorders and develop better treatments. In fact, this approach has already proven itself with the finding that the genes which control circadian rhythms in fruit flies, also control the timing of human sleep and can malfunction in certain human circadian sleep disorders. Researchers at Penn are actively searching for additional genes that control sleep and wakefulness in fruit flies and round worms.

 


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