A new brain-imaging study in mice suggests that sleep may not help clear toxins and daily waste from the brain, calling into question what scientists have called a “Nobel Prize-winning idea” in of neuroscience.
“The field has focused so much on the idea of clearance as one of the main reasons we sleep, that we were very surprised to observe the opposite in our results,” says Nick Franks, a neuroscientist at the Imperial College London (ICL) who co-led the study. -directed the study.
Sleep, while mysterious, has many possible benefits, from consolidating memories to improving mental health, that we shouldn’t ignore.
But following on from the (now contested) amyloid hypothesis, which describes how clumps of proteins build up in the brains of people with Alzheimer’s disease, sleep is thought to help the brain eliminate waste from the day.
Decades of research have also linked sleep, protein clearance and Alzheimer’s disease. As a result, sleep has been identified as a key modifiable risk factor for Alzheimer’s disease, the most common form of dementia, although the relationship is complicated: poor sleep could be a contributing factor to Alzheimer’s disease. Alzheimer’s or a symptom thereof.
A single animal study certainly isn’t going to overturn mountains of research linking sleep, proteins, and neurodegenerative diseases, but given these complexities, it could prompt further investigation.
The researchers injected a fluorescent dye into the brains of mice, watched it spread, and measured the rate of clearance when the animals were awake, asleep, and under anesthesia.
They cross-referenced their imaging results with other measurements on “brain ghost” gels composed of agarose and slices of mouse brain tissue, collected at different times.
“Our results challenge the idea that the essential function of sleep is to remove toxins from the brain,” the researchers write in their article.
“We found that the rate of dye removal from the brain was significantly reduced in animals that were asleep or under anesthesia,” adds Frank.
Previous research has established that using tracer dyes is a fair method for estimating the rate at which fluids flow through the brain, a process that we believe washes away proteins and other waste products.
However, even though the massive flow of fluid may increase in the brain during sleep, this does not mean that the brain is removing waste from the fluid. Some findings support this idea, while others, like the current results, call it into question.
Additionally, the size of molecules in the fluid can affect how quickly they move through the brain and through which channels. The different fluorescent dyes used in this study weighed much less than the clumps of misfolded proteins that accumulate in Alzheimer’s, Parkinson’s, and other neurodegenerative diseases.
The study also focused primarily on the flow of bulk fluid through the brain, the so-called glymphatic system, while other mechanisms – namely an intracellular “waste disposal” system – play a role. important in the elimination of lumpy proteins.
Still, the results are worth considering: The brains of sleeping mice cleared the green fluorescent dye 30% slower than those of awake animals, and anesthesia slowed clearance from the brains by 50%.
“At the moment, we don’t know what in these states slows the elimination of molecules from the brain (via the glymphatic system),” says Franks. “The next step in our research will be to try to understand why this happens.”
Despite these results, the researchers do not say that they diminish the importance of sleep. Up to 44 percent of Alzheimer’s patients suffer from sleep problems, as do 90 percent of people with dementia with Lewy bodies or Parkinson’s disease.
“Sleep disturbances are a common symptom in people with dementia, but we still don’t know whether it is a consequence or a determining factor in the progression of the disease,” says Bill Wisden, molecular neuroscientist at ICL and author of the study.
“It may well be that getting good sleep helps reduce the risk of dementia for reasons other than eliminating toxins.”
The study was published in Natural neuroscience.
News Source : www.sciencealert.com
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