[新知] 睡眠與清醒的鑰匙?
這篇研究發現GABA和Histamine的關係. Histamine可以促進清醒, 而GABA是為了避免過於
清醒的負回饋機制. 在實驗中, 小鼠若沒了GABA, 則會顯示異常的具有活動力, 活動時間
變長, 深度睡眠減少. 最重要的是, 一般老鼠在睡眠剝奪之後通常要更長的睡眠時間, 但
缺少GABA的小鼠則無此現象, 依然生龍活虎. 下一步, 該研究團隊要進一步觀察是否這些
小鼠會有認知與記憶能力的衰退.
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Study finds brain chemicals that keep wakefulness in check
網址:
http://medicalxpress.com/news/2015-07-brain-chemicals.html
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 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.
Professor Wisden said, "Sleep is essential for health. We have to do it every
day. But nobody yet knows why."
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.
More information: "Wakefulness Is Governed by GABA and Histamine
Cotransmission," Neuron (2015), DOI: 10.1016/j.neuron.2015.06.003
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