Study: Sleep Clears
Brain of Molecules Associated With Neurodegeneration
 |
| Scientists watched dye flow through the brain of a sleeping mouse. (Credit: Courtesy of Nedergaard Lab, University of Rochester Medical Center) |
"Sleep
changes the cellular structure of the brain. It appears to be a completely
different state," said Maiken Nedergaard, M.D., D.M.Sc., co-director of
the Center for Translational Neuromedicine at the University of Rochester
Medical Center in New York, and a leader of the study.
For
centuries, scientists and philosophers have wondered why people sleep and how
it affects the brain. Only recently have scientists shown that sleep is
important for storing memories. In this study, Dr. Nedergaard and her
colleagues unexpectedly found that sleep may be also be the period when the
brain cleanses itself of toxic molecules.
Their
results, published in Science, show that during sleep a plumbing
system called the glymphatic system may open, letting fluid flow rapidly
through the brain. Dr. Nedergaard's lab recently discovered the glymphatic
system helps control the flow of cerebrospinal fluid (CSF), a clear liquid
surrounding the brain and spinal cord.
"It's
as if Dr. Nedergaard and her colleagues have uncovered a network of hidden
caves and these exciting results highlight the potential importance of the
network in normal brain function," said Roderick Corriveau, Ph.D., a
program director at NINDS.
Initially
the researchers studied the system by injecting dye into the CSF of mice and
watching it flow through their brains while simultaneously monitoring
electrical brain activity. The dye flowed rapidly when the mice were
unconscious, either asleep or anesthetized. In contrast, the dye barely flowed
when the same mice were awake.
"We
were surprised by how little flow there was into the brain when the mice were
awake," said Dr. Nedergaard. "It suggested that the space between
brain cells changed greatly between conscious and unconscious states."
To
test this idea, the researchers used electrodes inserted into the brain to
directly measure the space between brain cells. They found that the space
inside the brains increased by 60 percent when the mice were asleep or
anesthetized.
"These
are some dramatic changes in extracellular space," said Charles Nicholson,
Ph.D., a professor at New York University's Langone Medical Center and an
expert in measuring the dynamics of brain fluid flow and how it influences
nerve cell communication.
Certain
brain cells, called glia, control flow through the glymphatic system by
shrinking or swelling. Noradrenaline is an arousing hormone that is also known
to control cell volume. Similar to using anesthesia, treating awake mice with
drugs that block noradrenaline induced unconsciousness and increased brain
fluid flow and the space between cells, further supporting the link between the
glymphatic system and consciousness.
Previous
studies suggest that toxic molecules involved in neurodegenerative disorders
accumulate in the space between brain cells. In this study, the researchers
tested whether the glymphatic system controls this by injecting mice with
labeled beta-amyloid, a protein associated with Alzheimer's disease, and
measuring how long it lasted in their brains when they were asleep or awake.
Beta-amyloid disappeared faster in mice brains when the mice were asleep,
suggesting sleep normally clears toxic molecules from the brain.
"These
results may have broad implications for multiple neurological disorders,"
said Jim Koenig, Ph.D., a program director at NINDS. "This means the cells
regulating the glymphatic system may be new targets for treating a range of
disorders."
The
results may also highlight the importance of sleep.
"We
need sleep. It cleans up the brain," said Dr. Nedergaard.
Story Source:
The
above story is based on materials provided byNIH/National Institute of Neurological Disorders and
Stroke.
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Journal Reference:
- 1. L. Xie, H. Kang, Q. Xu, M. J. Chen, Y. Liao, M. Thiyagarajan, J. O'Donnell, D. J. Christensen, C. Nicholson, J. J. Iliff, T. Takano, R. Deane, M. Nedergaard. Sleep Drives Metabolite Clearance from the Adult Brain. Science, 2013; 342 (6156): 373 DOI: 10.1126/science.1241224
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NIH/National Institute of Neurological Disorders and Stroke (2013,
October 17). Brain may flush out toxins during sleep; Sleep clears brain of
molecules associated with neurodegeneration: Study. ScienceDaily.
Retrieved October 19, 2013, from http://www.sciencedaily.com/releases/2013/10/131017144636.htm