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THE SCIENCE OF SLEEPING |
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> An essay on the science of sleeping |
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Control of Sleep and Body Temperature
As anyone who has had a cold recently can testify, the response to infection
includes both a fever and drowsiness. And anyone who has tried to sleep through
a hot, sticky summer night will realize that sleep and control of body
temperature are intertwined. Recent work in the laboratory of Clifford Saper, in
the Department of Neurology at Beth Israel Hospital, is beginning to make sense
of this connection.
His group monitors the cell groups in the rodent brain that are turned on
during physiological responses. By using carefully controlled physiological
stimuli and watching for evidence of a protein called Fos, a product of the gene c-fos, expressed when neurons are activated, investigators can both
monitor which neurons are activated and simultaneously determine the connections
and neurotransmitters that are used.
Saper's group finds that, in a brain structure, the hypothalamus, known to
command many automatic body functions, there are two adjacent cell groups that
share many connections. One, the ventrolateral preoptic nucleus, seems to be
responsible for sleep and, in fact, is the only cell group in the brain that
shows Fos-activation during sleep. The other, the ventromedial preoptic area, is
thought to be involved in thermoregulation/fever.
Studies of the two areas' connections suggest that both may use the same
neurotransmitter, called GABA, one to inhibit the brain's arousal system,
allowing sleep to occur, and the other to inhibit warm-sensitive cells that act
as a thermostat. Activation of the ventromedial preoptic area can "fool" the
thermostat into thinking body temperature is lower than it actually is, and
cause excess heat production. Both cell groups are activated during fever caused
by immune stimulation, producing the characteristic elevation of body
temperature and sleepiness.
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