Brain switch that says 'it is time to sleep' found

Date: Feb-26-2014Researchers at the University of Oxford in the UK have discovered the molecular

switch in the brain that sends us to sleep.

Although the researchers worked on fruit flies for their study, they believe a similar mechanism exists in human brains.

The discovery took place in the laboratory of senior author Prof. Gero Miesenböck at

Oxford's Centre for Neural Circuits and Behaviour (CNCB).

Two mechanisms regulate our sleep: one takes into account the external environment, and the

other monitors the internal environment.

The mechanism that links to the external environment is the body clock, which attunes humans and

other animals to the 24-hour day-night cycle.

Researchers studied the internal homeostat that monitors sleep deficit

Researchers have discovered that a molecular switch in the brain that tells us when it is time to sleep.

This new study investigates a "homeostat" mechanism that is attuned to the internal environment

and monitors what is happening in the brain. This keeps track of waking hours and tells us when

it is time to sleep and reset. It is as though sleep deficit builds up, reaches a point that

turns the switch on, and we then start to nod off.

Prof. Miesenböck says:

"What makes us go to sleep at night is probably a combination of the two mechanisms. The body

clock says it's the right time, and the sleep switch has built up pressure during a long waking

day."

He and his colleagues found the switch works by controlling a handful of sleep-promoting

neurons that are active when we are tired and need to sleep, and quieten down when we are fully

rested.

One of the lead authors, Dr. Jeffrey Donlea - who specializes in testing new

scientific ideas in flies at the CNCB - explains that although they made this new discovery in flies:

"There is a similar group of neurons in a region of the human brain. These neurons are also

electrically active during sleep and, like the flies' cells, are the targets of general

anesthetics that put us to sleep. It's therefore likely that a molecular mechanism similar to

the one we have discovered in flies also operates in humans."

The researchers worked with mutant flies to find the critical part of the sleep switch. They

discovered that when certain genes were silenced, the mutant flies could not catch up on lost sleep

after they were kept awake all night.

Mutant flies helped researchers discover key mechanism in the sleep homeostat

Prof. Miesenböck likens the sleep homeostat to the thermostat that controls central heating

in the home:

"A thermostat measures temperature and switches on the heating if it's too cold. The sleep

homeostat measures how long a fly has been awake and switches on a small group of specialized

cells in the brain if necessary. It's the electrical output of these nerve cells that puts the

fly to sleep."

The researchers found a key molecular component was disabled in the electrical circuit of the

mutant flies that kept the sleep-inducing neurons permanently switched off.

The study is important because it may help identify new targets to improve treatments for

sleep disorders like insomnia.

However, as the researchers point out, there is still a way to go before any solutions can

move from the lab into the clinic.

They also hope that exploring this mechanism and its role further could help answer the big

question: "What is the purpose of sleep?"

As a next step, the researchers plan to investigate what internal signal triggers the switch in the

first place. They also want to answer questions such as, "What are the sleep-promoting cells monitoring while we

are awake?"

Research at the CNBC is funded by the Wellcome Trust and the Gatsby Charitable Foundation,

while additional funds from the UK Medical Research Council, the US National Institutes of

Health and the Human Frontier Science Program helped finance this particular study, which is published in the journal

Neuron.

Medical News Today recently reported on a study suggesting that

a good night's sleep may be

essential to brain health. Swedish researchers found that depriving healthy young men of a night's sleep

increased blood concentrations of brain molecules to levels seen in brain damage.

Written by Catharine Paddock PhD




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