January 11, 2008
Round Worms Help Explain Purpose Of Sleep
The roundworm C. elegans may be the key in unlocking the biological mystery of why we sleep. Researchers at the University of Pennsylvania's School of Medicine report that the round worm has a sleep-like state, joining most of the animal kingdom in displaying this physiology.
This research has implications for explaining the evolution and purpose of sleep and sleep-like states in animals. Additionally, genetic work associated with the study provides new prospects in identifying sleep-regulatory genes and drug targets for sleep disorders.
The research showed there is a period of behavioral dormancy during the worm's development called lethargus that has sleep-like properties. "Just as humans are less responsive during sleep, so is the worm during lethargus," explains the study's first author David M. Raizen, MD, PhD, Assistant Professor of Neurology, "And, just as humans fall asleep faster and sleep deeper following sleep deprivation, so does the worm."
By demonstrating that worms sleep, Raizen and colleagues have not only demonstrated the ubiquity of sleep in nature, but also propose a compelling hypothesis for the purpose of sleep.
Because the time of lethargus coincides with a time in the round worms' life cycle when synaptic changes occur in the nervous system, they propose that sleep is a state required for nervous system plasticity. In other words, in order for the nervous system to grow and change, there must be downtime of active behavior. Other researchers at Penn have shown that, synaptic changes in mammals occur during sleep and that sleep deprivation disrupts these synaptic changes.
Additionally, the research team used C. elegans to identify a gene that regulates sleep. This gene has been previously studied but not suspected to play a role in sleep regulation. However, the findings suggest a potential role for this gene in regulating human sleep and may provide a pathway for developing new treatments for sleep disorders.
"It opens up an entire new line of inquiry into the functions of sleep," said Penn Center for Sleep Director and co-author Allan I. Pack, MB, Chb, PhD. The report was published in this week's advanced online edition of Nature.
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