Saturday, November 5, 2011

Brain cells that keep us awake uncovered

A group of cells located in a brain area called the hypothalamus, involved with receiving various sensory input, is responsible for keeping us awake, a new study has shown. By releasing a chemical messenger, they keep our body in an aroused state, under the influence of day light. It was already known that light influences our behavioural state, but the brain cells that are associated with translating day light to a message of keeping us awake were previously unknown. This study sheds light on why people are narcoleptic, a disease in which patients are always sleepy and drowsy, which is associated with a loss of this particular messenger.

The cells in the hypothalamus release hypocretin, the chemical messenger, or neurotransmitter, responsible for keeping us in an aroused state. A study was performed in mice to uncover the functions of hypocretin: the researchers showed that lacking hypocretin rendered mice unable to stay awake in the light and work for food rewards, as opposed to normal, wildtype mice. In the dark, there was no difference between the two groups, showing that hypocretin functions in our behaviour to be awake during daylight, and asleep during the night, as part of our biological clock.

Failure to respond to light is found in narcoleptics, who are constantly sleepy, and suffer from 'sleep attacks'. By administering hypocretin, it may be possible to restore the normal wake-sleep cycle set by our biological clock. It also seems that by discovering the function of hypocretin, the underlying disease mechanism of narcolepsy has been found, though seperate studies are needed to confirm whether narcoleptics can improve by administering hypocretin to the brain. Many common symptoms of narcolepsy are not explained by hypocretin though: many patients have sudden outbursts of heavy emotions, which can consequently lead to loss of muscle strength, causing them to fall flat out on the floor.

On the other hand, blocking the actions of hypocretin could help a different set of patients; those who suffer from insomnia. An overly active hypocretin response of the body could be an underlying cause in insomnia, although this hypothesis needs to be experimentally assessed.

In a previous study, scientists found a gene that codes for a key protein called JARID1a regulating our biological clock, by inducing the wake state. It is part of a complex circadian internal circuit that responds to the suprachiasmatic nucleus, which is the part of the brain that sets our daily rhythm, also in response to light.

It goes to show that rhythmically affecting our behaviour in terms of sleep and wake is caused by a complex set of interactions in our brain. By unveiling the mechanisms behind it, we may find cues for the development of new drugs to counter diseases found to be associated with a faulty rhythm, as has been shown with narcolepsy.

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