Despite much progress in our understanding of C. elegans locomotion and
navigation, little is
known about the regulation of the absence of movement. Yet behavioral quiescent
states are
universal to the animal world, with the most famous and mysterious of these
being sleep. In a
famous example of studying a sleep-like behavior in a phylogenetically ancient
model organism,
Seymour Benzer - physicists, biologists and one of the founders of the field of
molecular biology
of behavior - studied the cycles of quiescence of the fruit fly Drosophila. He
showed that the
period gene was a key regulator of the circadian clock, which was found to have
a role in
regulating sleep in mammals. Recently, additional pathways were implicated in
regulating sleeplike
behavior in fruit flies and sleep in mice, rabbits and hamsters: Epidermal
Growth Factor
(EGF) signaling and cyclic-Adenosine MonoPhosphate (cAMP) signaling.
The roundworm C. elegans is in many ways a simpler model organism than the fruit
fly. It
has only 302 neurons (the connections of which have been anatomically mapped), a
short life
cycle and an optically transparent body. The worm develops through four larval
stages before it
reaches adulthood. At the end of each of these stages it exhibits a quiescent
behavior called
lethargus. David Raizen et al. recently demonstrated that lethargus bears
behavioral similarities
to sleep, such as reversibility (the worms "wake up"), sensory gating (an
elevated threshold for
responding to sensory stimuli) and homeostatic control (following deprivation,
lethargus is
resumed faster and "deeper"). Curiously, lethargus is also phase-locked with
cycles in the
expression of the worm′s period homologous gene. Moreover, EGF and cAMP
signaling both
appear to have roles in regulating lethargus that resemble their regulation of
similar behaviors in
flies and mammals. Taken together, these observations suggest a possible ~6x108
year-old
genetic link between these phenomena.
I will discuss the opportunities, challenges and risks of studying a sleep-like
behavior using
C. elegans as a model system, and present preliminary results from our
behavioral analysis. Time
permitting, I will discuss some tools and ideas that physics can bring to the
study of this
everyday natural phenomenon.