Study: Why We Get Sleepy

LiveScience Staff, LiveScience.com

Scientists know we need sleep, but they don't know

exactly why, and they've been pretty clueless about how

the brain decides when to sleep.

Some of the mystery has been put to rest. A new study of

mice finds that brain cells called astrocytes fuel the urge

to sleep by releasing adenosine, a chemical known to

have sleep-inducing effects that can be inhibited by

caffeine.

The longer a person or animal is awake, the stronger the

urge to sleep becomes. This is known as sleep pressure.

Prior studies pointed to adenosine as a trigger for sleep

pressure. The chemical accumulates in the brain during

waking hours, eventually helping to stimulate the unique

patterns of brain activity that occur during sleep.

The new study found "adenosine from astrocytes clearly

regulates sleep pressure," said study team member

Michael Halassa of Tufts University School of Medicine in

Boston.

It is the first time a non-neuronal cell in the brain has been

shown to influence behavior, Halassa said. Unlike

neurons, astrocytes do not fire electrical spikes, and they

are often thought of as simply support cells.

"This research could lead to better drugs for inducing

sleep when it is needed, and for staving off sleep when it

is dangerous," said Merrill Mitler of the National Institute

of Neurological Disorders and Stroke, part of the federally

funded National Institutes of Health.

The research is detailed today in the journal Neuron.

The scientists flipped a genetic switch in the mice to block

the release of adenosine and other chemicals from

astrocytes. The researchers then deprived the mice of

sleep for short periods, and evaluated them with

behavioral tests and by recording brain activity.  

Mice subjected to the genetic blockade exhibited less

sleep pressure than control mice. Following sleep

deprivation, they did not need as much compensatory

sleep, and during the early phases of sleep , they had

patterns of brain activity consistent with low sleep

pressure.

Further studies of the newfound sleep mechanism in mice

could help reveal why people need sleep at all, the

scientists said.

·           5 Things You Must Know About Sleep 

·           How Long Can a Person Survive Without Sleep? 

·           Sleep News and Information 

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