Snoozing Worms Help Explain Evolution Of Sleep


Researchers at the University of Pennsylvania School of Medicine
report that the
round worm C. elegans has a sleep-like state. (Credit: Margaret
Higgins,
University of Pennsylvania School of Medicine)ScienceDaily (Jan. 15,
2008) -
The roundworm C. elegans, a staple of laboratory research, may be key
in
unlocking one of the central biological mysteries: why we sleep.
Researchers at
the University of Pennsylvania School of Medicine report in the
January 11
advanced online edition of Nature 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.

In addition, genetic work associated with the study provides new
prospects for
the use of C. elegans to identify sleep-regulatory genes and drug
targets for
sleep disorders.

First author David M. Raizen, MD, PhD, Assistant Professor of
Neurology, in
collaboration with other researchers at the Penn Center for Sleep,
showed that
there is a period of behavioral quiescence 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 Raizen. "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 for 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 down time of
active
behavior. Other researchers at Penn have shown that, in mammals,
synaptic
changes occur during sleep and that deprivation of sleep results in a
disruption
of these synaptic changes.

In addition, the research team used C. elegans as a model system to
identify a
gene that regulates sleep. This gene, which encodes a protein kinase
and is
regulated by a small molecule called cyclic GMP, has been previously
studied but
not suspected to play a role in sleep regulation. The findings suggest
a
potential role for this gene in regulating human sleep and may provide
an avenue
for developing new drugs for sleep disorders.

"It opens up an entire new line of inquiry into the functions of
sleep," notes
Penn Center for Sleep Director and co-author Allan I. Pack, MB, Chb,
PhD.

The Center for Sleep and Respiratory Neurobiology at the University of
Pennsylvania is a multidisciplinary center dedicated to exploring and
understanding the basic mechanism of sleep and circadian rhythm, the
pathogenesis of sleep disorders, and the outcomes of therapy.

In addition to Raizen and Pack, co-authors are John E. Zimmerman,
Matthew H.
Maycock, Uyen D, Ta, Meera V. Sundaram, all from Penn, and Young-jai
You from
the University of Texas Southwestern Medical Center (Dallas). The
research was
supported by grants from the National Institute of Neurological
Disorders and
Stroke, the National Heart Lung and Blood Institute, and the National
Alliance
for Research on Schizophrenia and Depression.

Adapted from materials provided by University of Pennsylvania School
of
Medicine.

University of Pennsylvania School of Medicine (2008, January 15).
Snoozing Worms
Help Explain Evolution Of Sleep. ScienceDaily. Retrieved January 16,
2008, from
http://www.sciencedaily.com/releases/2008/01/080111100622.htm