Quality of Waking
Hours Determines Ease of Falling Sleep
From
ScienceDaily.com
The
quality of wakefulness affects how quickly a mammal falls asleep, UT
Southwestern Medical Center researchers report in a study that identifies two
proteins never before linked to alertness and sleep-wake balance.
"This
study supports the idea that subjective sleepiness is influenced by the quality
of experiences right before bedtime. Are you reluctantly awake or excited to be
awake?" said Dr. Masashi Yanagisawa, professor of molecular genetics and a
Howard Hughes Medical Institute investigator at UT Southwestern. He is
principal author of the study published online in May in the Proceedings of
the National Academy of Sciences.
Co-author Dr. Robert Greene, UT Southwestern professor of psychiatry and a physician at the Dallas VA Medical Center, said the study is unique in showing that the need for sleep (called sleep homeostasis) can be separated from wakefulness both behaviorally and biochemically, meaning the two processes can now be studied individually.
"Two
of the great mysteries in neuroscience are why do we sleep and what is sleep's
function? Separating sleep need from wakefulness and identifying two different
proteins involved in these steps represents a fundamental advance," he
said.
If
borne out by further research, this study could lead to new ways of assessing
and possibly treating sleep disorders, perhaps by focusing more attention on
the hours before bedtime because the quality of wakefulness has a profound
effect on sleep, Dr. Yanagisawa said.
The
experiment featured three groups of mice with virtually identical genes. The
control group slept and woke at will and followed the usual mouse pattern of
sleeping during the day and being awake at night. The two test groups were
treated the same and had the same amount of sleep delay -- six hours -- but
they were kept awake in different ways, said lead author Dr. Ayako Suzuki, a
postdoctoral researcher who works in the laboratories of both Dr. Yanagisawa
and Dr. Greene.
The
first test group's sleep was delayed by a series of cage changes. Mice are
intensely curious, so each cage change was followed by an hour spent vigorously
exploring the new surroundings. This behavior would roughly correspond to
teenagers voluntarily delaying bedtime with a new and stimulating event like a
rock concert or video game.
Researchers
kept the second group awake as gently as possible, usually by waving a hand in
front of the cage or tapping it lightly whenever the mice appeared to be
settling down to sleep. That test group would more resemble parents reluctantly
staying awake awaiting a child's return from a concert.
Both
test groups experienced the same amount of sleep deprivation, but their
reactions to the different forms of alertness were striking, Dr. Yanagisawa
said. In one test, the cage-changing group took longer to fall asleep than the
gentle-handling group even though an analysis of their brain waves indicated
equal amounts of sleep need in both test groups.
"The
need to sleep is as high in the cage-changing group as in the gentle-handling
group, but the cage-changers didn't feel sleepy at all. Their time to fall asleep
was nearly the same as the free-sleeping, well-rested control group," he
said.
The
researchers identified two proteins that affected these responses, each linked
to different aspects of sleep: phosphorylated dynamin 1 levels were linked to
how long it took to fall asleep, while phosphorylated N-myc downstream
regulated gene 2 protein levels tracked the amount of sleep deprivation and
corresponded to the well-known brain-wave measure of sleep need, they report.
"The
two situations are different biochemically, which is a novel finding," Dr.
Yanagisawa said, adding, "These proteins are completely new to sleep
research and have never before been linked to sleep need and wakefulness."
From
an evolutionary perspective, an arousal mechanism that adapts to environmental
stimuli is crucial because sleeping on a rigid schedule could be dangerous.
"Animals, including humans, must be able to keep themselves at least
temporarily alert, say during a natural disaster," he said.
Drs.
Yanagisawa and Greene are both corresponding authors on the study, and both
have dual appointments at the International Institute for Integrative Sleep
Medicine, University of Tsukuba, Tsukuba, Japan. Former Associate Professor of
Internal Medicine Dr. Christopher M. Sinton, now at the University of Arizona,
was also involved in the study.
The
study was funded by the Japan Society for the Promotion of Science through the
Funding Program for World-Leading Innovative R&D on Science and Technology;
the Perot Family Foundation; and the Department of Veterans Affairs.
Story Source:
The
above story is reprinted from materials provided by UT
Southwestern Medical Center.
Note: Materials may be edited for content and length. For further
information, please contact the source cited above.
Journal Reference:
1.
A. Suzuki, C. M. Sinton,
R. W. Greene, M. Yanagisawa.Behavioral and biochemical dissociation of
arousal and homeostatic sleep need influenced by prior wakeful experience in
mice. Proceedings of the National Academy of Sciences, 2013;
DOI: 10.1073/pnas.1308295110
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UT Southwestern Medical Center (2013, June 17). Quality of waking
hours determines ease of falling sleep. ScienceDaily. Retrieved
June 18, 2013, from http://www.sciencedaily.com/releases/2013/06/130617173133.htm
