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Can’t Sleep? Turn on the Sleep Switch!

Sleeping manResearchers at Oxford University’s Center for Neural Circuits and Behavior identified the switch in the brain that sends us off to sleep in a study in fruit flies. Although the study was carried out in fruit flies (Drosophila), the researchers say the sleep mechanism is likely to be relevant to humans. This study has been published on Neuron.

The sleep switch works by regulating the activity of a battery of sleep-promoting nerve cells, or neurons, in the brain. When we are tired and need sleep, the neurons fire; when we are fully rested, they dampen down.

 “When you feel tired, the neurons in your brain shout loud and send you to sleep,” says Professor Gero Miesenböck at Oxford University, in whose laboratory the new study was carried out.

Our body has two mechanisms to regulate sleep. One is the body clock, which attunes animals and humans to the 24 hour cycle of day and night. The other one is the sleep “homeostat”, which is a device in the brain that maintains track of our waking hours and put us to sleep when we need to reset. This mechanism indicates an internal nodding off point that is separate from external factors. When it’s switched off or out of use, sleep deficits will build up.

Professor Miesenböck says: “It is probably a combination of the two mechanisms that makes us go to sleep at night. The body clock says it is the right time, and the sleep switch has built up pressure during a long waking day.”

The study on fruit flies allowed the researchers to discover the critical part of the sleep switch. Jeffrey Donlea says: “We found mutant flies that can’t catch up on their lost sleep after they had been kept awake all night.”

Fruit flies stop moving when they go to sleep and they require more disturbance to get them up. If flies are deprived of sleep, they are prone to nodding off and are impaired cognitively – they experience severe learning and memory deficits, much as sleep deprivation in humans leads to problems.

Professor Miesenböck says: “The sleep homeostat is very similar to the thermostat in your home. A thermostat measures the temperature and switches to heating when it is too cold. Similarly, the sleep homeostat measures how long a fly have been awake and if necessary, switches on a small groups of specialized cells in the brain. These nerve cells send out electrical output and put the fly to sleep.”

In the mutant flies, the researchers managed to demonstrate a key molecular component of the electrical activity switch is broken and the sleep-including neurons are always off, resulting in insomnia.

 “There is a similar group of neurons in a region of the human brain. The neurons are also electrically active during sleep and, like the flies’ cells, are the targets of general anaesthetics that put us to sleep. Therefore, it is likely that a molecular mechanism similar to the one we have found in flies also operates in humans,” explains Dr Jeffrey Donlea, one of the lead authors of the study.

The researchers believe that pinpointing the sleep switch may help people identify new targets for novel drugs, providing potential treatments for sleep disorders.

There is much research work to do. The further research could give insight into the big unanswered question of why people need to sleep at all. The other lead author of the study, Dr. Diogo Pimentel at Oxford University, says: “The big question now is to figure out what internal signal the sleep switch responds to. What do these sleep-promoting cells monitor when we are awake?”

 “If we learn what happens in our brain during waking that needs sleep to reset, we may get closer to solving the mystery of why animals need to sleep.”

Source: EurekAlert!