Mice that have a particular brain chemical switched
off become hyperactive and sleep for just 65 per
cent of their normal time.
This discovery, published in the journal Neuron,
could help researchers to develop new drugs that
promote better sleep, or control hyperactivity in
people with the medical condition mania.
Scientists altered the neurochemistry of mice to
help investigate why we need to sleep, what controls
our wakefulness, and how a balance between these two
states influences brain functions like concentration
and memory and our general health.
The chemicals they studied, histamine and GABA, are
produced in a primitive part of the brain, the
hypothalamus, that is highly similar in mice and
humans.
The team of scientists was led by Dr Stephen
Brickley, Professor Nick Franks and Professor Bill
Wisden from the Department of Life Sciences and the
Centre for Neurotechnology at Imperial College
London.
Scientists already know the chemical histamine sends
signals to the brain to make it awake, which is why
antihistamines are associated with drowsiness.
The new research suggests that the chemical GABA
acts against histamine, like a chemical 'brake'
preventing wakefulness being too intense.
The researchers found that GABA and histamine are
made in the same brain cells, called histamine
neurons, which led the scientists to question its
function.
They altered the levels of the GABA produced by the
mice's brains and measured what changes this had on
their brain activity over the day and night.
Mice without the GABA chemical developed
characteristics similar to a medical condition
called mania, in which patients experience
restlessness and sleeplessness. In humans these are
often also symptoms of bipolar disorder, which
affects around 2.4 million people in the UK.
"Wakefulness stimulated by histamine may be too much
of a good thing, and so the brain has a built in
brake on histamine's wake-inducing actions," said Dr
Brickley.
The scientists found that compared with normal mice,
those without GABA ran twice as far and twice as
fast, and maintained or even increased their overall
activity over a 30 minute period.
The mice also stayed awake much longer in the day,
when they would otherwise be asleep. When they did
sleep, the mice experienced just 65 per cent of the
normal amount of non-REM (Rapid Eye Movement) sleep,
a heavy sleep state with no dreaming.
"What particularly surprised us was how little the
mice were affected by sleep deprivation," said
Professor Franks.
"Normally mice that lose 5 hours of sleep would
sleep for longer following this deprivation, and we
would see a much lower level of activity. These mice
kept up their hyperactive state over the following
16 hours they were awake. They didn't appear to need
any recovery sleep at all."
The scientists have begun new work with mice to
investigate the link between lack of sleep and
memory loss. They hope this will lead to a better
understanding of the link between poor sleep and
mental health issues in humans.
See also
Neuron loss in schizophrenia and depression could be
prevented with an antioxidant (2013-06-12)
link...
OHSU scientists discover new role for vitamin C in
the eye and the brain (18/07/2011)
link...
A gene mutation for excessive alcohol drinking found
(2013-12-05)
link...
NIH study identifies gene variant linked to
compulsive drinking (2015-07-26)
link...
For more information
Yu et al., Wakefulness Is Governed by GABA and
Histamine Cotransmission, Neuron (2015),
doi:10.1016/j.neuron.2015.06.003
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