Science News - July 21, 2018

F R O M TO P : E . OT WE L L; M . NE D E RG A A R D

calm. Especially if you do it during the daytime
when they are supposed to be sleeping, and they
are warm and you give them sugar water. They’re
not afraid.”
The day of the experiment, the scientists made
a hole in the mice’s skulls, placed a cover over it
and injected a dye to measure cerebrospinal fluid
in the brain. During sleep, the spaces between
the brain cells widened by about 60 percent and
allowed more fluid to wash through, taking the
metabolic debris, including A-beta, with it.

“It’s like the dishwasher turned on,” Nedergaard says. She named this phenomenon the “glymphatic system” because it appears to be controlled by glial cells, brain cells that help insulate neurons and perform much of the brain’s routine maintenance work (SN: 8/22/15, p. 18).

Similar observations of cerebrospinal fluid circulation have been carried out in people, but with less invasive ways of measuring. In one, researchers from Oslo University Hospital, Rikshospitalet compared 15 patients who had a condition called normal pressure hydrocephalus, a kind of dementia caused by buildup of cerebrospinal fluid in the cavities of the brain, with eight people who didn’t have the condition.

The researchers used a tracer for cerebrospinal
fluid and magnetic resonance imaging to measure
the flow over 24 hours. Immediately after a night’s
sleep, cerebrospinal fluid had drained in healthy
people but lingered in the patients with dementia,
the researchers reported in Brain in 2017.

Don’t snooze, you lose?

The central question — the one that doctors really want to answer — is whether better sleep could treat or even prevent Alzheimer’s. To try to figure this out, Bendlin and her Wisconsin colleagues are now studying people with sleep apnea. People with that condition stop breathing during the night, which wakes them up and makes for a lousy night’s sleep. A machine called a CPAP, short for continuous positive airway pressure, treats the condition.

“Once people start treatment, what might we
see in the brain? Is there a beneficial effect of
CPAP on markers of Alzheimer’s?” Bendlin won-
ders. “I think that’s a big question because the
implications are so large.”
A study reported in Neurology in 2015 offers
a reason to think CPAP might help. Using data
from almost 2,500 people in the Alzheimer’s
Disease Neuroimaging Initiative, researchers at
the New York University School of Medicine found
that people with sleep disorders like obstructive
sleep apnea showed signs of mild cognitive prob-
lems and Alzheimer’s disease at younger ages than
those who did not. But for those who used CPAP,
onset of mild cognitive problems was delayed.

“If we find out that sleep problems contribute to brain amyloid — what that really says is there may be a window to intervene,” Bendlin says. And the solution — more attention to sleep — is one prescription with no side effects. s

Explore more

s Yumna Saeed and Sabra M. Abbott. “ Circadian disruption associated with Alzheimer’s Disease.” Current Neurology and Neuroscience Reports. April 2017.

Flow of cerebrospinal fluid in a mouse’s brain is much higher during sleep (left, red) than when the animal is awake (right, green).

Cerebrospinal
fluid
Interstitial
fluid
Cerebrospinal
fluid carries
out waste
Skull

Go with the flow

One way the brain might clear out waste, including amyloid-beta, is via circulation of cerebrospinal and interstitial fluids. Fluid flows through the spaces in the brain, bathing neurons and eventually carrying debris out of the brain toward the liver. Studies suggest that this “glymphatic” circulation increases during sleep.