While sleep is recognised as vital for all animals with a nervous system, its precise biological function has remained enigmatic. Researchers at Bar-Ilan University in Ramat Gan, Israel, found that broken DNA built up in the brains of zebrafish while they were awake, but that the accumulated damage was reduced after a long period of sleep.
'I think this is one of the key reasons we need to sleep,' said study author Professor Lior Appelbaum to the Guardian. 'An offline period gives us time to clean up everything for the next day, to give us a fresh start before we are busy with wakefulness again.'
The scientists flagged chromosomes with fluorescent markers that they could see under a microscope and used time-lapse imaging to track their movements during sleep cycles.
They were surprised to find that chromosomes in neuronal cells moved twice as fast while the zebrafish were asleep than when they were awake. They reasoned that this movement allowed the damaged DNA to reorganise and repair itself.
The study, published in Nature Communications, is one of several recent investigations into the importance of sleep. Poor sleep hygiene has been associated with adverse effects on health, such as weight gain (see BioNews 965) and decreased fertility (see BioNews 702). It as also been shown to increase risks of serious disorders such as cardiovascular disease and dementia. Identifying the biological events that occur in sleep may help us to understand why it is so important for our health.
Professor Appelbaum said that DNA damage accumulating in the brain was the 'price of wakefulness' and that animals use sleep as an opportunity to reduce this damage. Speaking to the Guardian, he proposed that: 'When we are very tired, neurons accumulate so much damage that they signal the whole brain that we have to go to sleep to fix the damage and avoid going into an unsafe zone.'