Researchers in the US have found that the brain’s natural waste clearance system is more active in sleeping mice than mice that are awake. The study, which showed that a hallmark Alzheimer’s protein was cleared faster during sleep, is published on Thursday 17 October in the journal Science.
A number of neurodegenerative diseases, including Alzheimer’s disease, are linked to the build-up of particular excess proteins in the brain. In healthy people, normal amounts of these proteins are present in the brain’s interstitial fluid – the fluid that surrounds brain cells – while excess proteins are cleared into the cerebrospinal fluid (CSF), which surrounds the brain and spinal cord.
Scientists at the University of Rochester, in New York, set out to investigate whether sleep may help regulate the activity of this natural clearance system. To do this the researchers studied mice that were awake, mice that were asleep and mice that had been anaesthetised. They found that the flow of CSF was greater in mice that were asleep compared to mice that were awake, while the volume of interstitial fluid was also greater in these mice.
Further investigation showed that when the mice were injected with amyloid – a key protein that accumulates in the brain during Alzheimer’s disease – this protein was cleared from the brain twice as fast in mice that were asleep, compared to mice that were awake.
Dr Simon Ridley, Head of Research at Alzheimer’s Research UK, the UK’s leading dementia research charity, said: