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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