16 November 2014

'Local' Clock in the Brain

All animals, from ants to humans, have internal 'circadian' clocks that respond to changes in light and tell the body to rest and go to sleep, or wake up and become active. A master clock found in part of the brain called the suprachiasmatic nucleus (SCN) is thought to synchronise lots of 'local' clocks that regulate many aspects of our metabolism, for example in the liver. But until now scientists have not had sufficient evidence to demonstrate the existence of these local clocks in the brain or how they operate. In a new study looking at mice, at Imperial College London and at the MRC Laboratory of Molecular Biology in Cambridge have investigated a local clock found in another part of the brain, outside the SCN, known as the tuberomamillary nucleus (TMN).
 

This is made up of histaminergic neurons, which are inactive during sleep, but release a compound called histamine during waking hours, which awakens the body. The researchers deleted a well-known 'clock' gene, Bmal1, from the histaminergic neurons and found that the mice produced higher levels of the enzyme that makes histamine and were awake for much longer periods than usual. The mice also experienced a more fragmented sleep, a shallower depth of sleep, and much slower recovery after a period of sleeplessness. This work with mice suggests that local body clocks play a key role in ensuring their sleeping and waking processes work properly. When a local clock was disrupted, their whole sleep and wake system malfunctioned.

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