Sleep 'boosts brain cell numbers'
Scientists believe they have discovered a new reason why weneed to sleep - it replenishes a type of brain cell.
Sleep ramps up the production of cells that go on to make aninsulating material known as myelin which protects our brain's circuitry.
The findings, so far in mice, could lead to insights aboutsleep's role in brain repair and growth as well as the disease MS, says theWisconsin team.
The work is in the Journal of Neuroscience.
Dr Chiara Cirelli and colleagues from the University ofWisconsin found that the production rate of the myelin making cells, immatureoligodendrocytes, doubled as mice slept.
The increase was most marked during the type of sleep that isassociated with dreaming - REM or rapid eye movement sleep - and was driven bygenes.
In contrast, the genes involved in cell death and stressresponses were turned on when the mice were forced to stay awake.
Precisely why we need to sleep has baffled scientists forcenturies. It's obvious that we need to sleep to feel rested and for our mindto function well - but the biological processes that go on as we slumber haveonly started to be uncovered relatively recently.
Growth and repair
Dr Cirelli said: "For a long time, sleep researchersfocused on how the activity of nerve cells differs when animals are awake versuswhen they are asleep.
"Now it is clear that the way other supporting cells inthe nervous system operate also changes significantly depending on whether theanimal is asleep or awake."
The researchers say their findings suggest that sleep lossmight aggravate some symptoms of multiple sclerosis (MS), a disease thatdamages myelin.
Scientists are only just unravelling the precise mysteries ofwhy we sleep
In MS, the body's immune system attacks and destroys themyelin coating of nerves in the brain and spinal cord.
Future studies could look at whether or not sleep affects thesymptoms of MS, says Dr Cirelli.
Her team is also interested in testing whether lack of sleep,especially during adolescence, may have long-term consequences for the brain.
Sleep appears necessary for our nervous systems to workproperly, says the US National Institute of Neurological Disorders and Stroke(NINDS).
Deep sleep coincides with the release of growth hormone inchildren and young adults. Many of the body's cells also show increasedproduction and reduced breakdown of proteins during deep sleep.
Since proteins are the building blocks needed for cell growthand for repair of damage from factors like stress and ultraviolet rays, deepsleep may truly be "beauty sleep", says NINDS.