The brain makes lots of waste. Now scientists think they know where it goes : Shots

The brain is home to around 170 billion cells and produces a lot of waste products as it carries out its normal tasks. To stay healthy, the brain needs to flush all of this waste out. But how exactly the brain does this remains a mystery.

Now, two teams of scientists have published three papers detailing the brain’s waste-clearance system, and their insights could help researchers better understand, treat, and even prevent a wide range of brain disorders.

All papers are published in this journal NatureIt has been suggested that during sleep, slow electrical waves force fluid around cells from deep within the brain to the surface, where a sophisticated interface allows waste products within to be absorbed into the bloodstream, carried to the liver and kidneys, and then removed from the body.

One of the waste products that is carried away is amyloid, a substance that forms sticky plaques in the brains of Alzheimer’s patients.

There is growing evidence that the brain’s waste removal system is impaired in Alzheimer’s disease, Jeffrey IliffHe studies neurodegenerative diseases at the University of Washington but was not involved in the study.

The new findings should help researchers understand exactly where the problem lies and perhaps solve it, Iliff says.

“Could restoring drainage prevent the onset of Alzheimer’s disease?” he asks.

A brief history of brainwashing

The new study is led by Iliff and Dr. Maiken NedergaardThe Danish scientist was the first to propose that the clear fluid in and around the brain is part of a system that flushes out waste products.

Scientists have Glymphatic System,of a body Lymphatic systemIt helps fight infection, maintain fluid levels, and filter waste and abnormal cells.

Both systems work like the plumbing in a house. Jonathan Kipnis He is a professor at Washington University in St. Louis and an author on two of the new papers.

“You have water pipes and sewer pipes,” Kipnis says, “clean water comes in, you wash your hands, dirty water comes out.”

However, the lymphatic system uses a network of tiny tubes that carry waste products into the bloodstream. The brain does not have these tubes.

So scientists have spent decades trying to answer a fundamental question, Kipnis said: “How do waste molecules leave the center of the brain, find their way to its borders, and eventually exit the body?”

Part of the answer came when Iliff and Nedergaard began proposing the glymphatic system in 2012 and 2013. They showed that in sleeping animals, cerebrospinal fluid begins to flow rapidly through the brain, flushing out waste products.

But what was pushing that fluid out, and how was it transporting waste products across the barrier that normally separates brain tissue from the bloodstream?

Washing Waves

Kipnis and his team set out to find out what the brain does while it sleeps, and as part of their research, they measured the strength of slow electrical waves that appear during animals’ deep sleep.

Then they noticed something: “By measuring the waves, we were also measuring the flow of interstitial fluid, which is the liquid in the space around the cells,” Kipnis says.

The team found that these waves act as signals, synchronizing the activity of neurons and turning them into tiny pumps that push fluid toward the brain’s surface. report February Journal Nature.

A second paper published in the same issue: NatureA team led by scientists from the Massachusetts Institute of Technology offered Further evidence that slow radio waves help remove waste products.

The researchers used mice with a form of Alzheimer’s disease and exposed them to bursts of sound and light that occurred 40 times per second.

This stimulation caused the animals to produce brain waves at the same low frequency.

Tests have shown that the waves increase the flow of clean cerebrospinal fluid into the brain and the flow of dirty fluid out of the brain, and that the fluid contains amyloid, a substance that builds up in the brains of people with Alzheimer’s disease.

In a paper published a few weeks ago, Kipnis display Waste products such as amyloid appear to be passing through the protective membrane that normally insulates the brain.

Kipnis and his team focused on the veins that pass through this membrane.

“There’s a sleeve around the vein, so it’s never completely sealed,” he says. [cerebrospinal fluid] It is excreted and sends waste products to the body’s lymphatic system.

From mice to humans

Together, the new research suggests that keeping the brain’s waste-clearance system functioning requires two distinct steps: pushing waste into the cerebrospinal fluid that surrounds the brain, and moving it into the lymphatic system so it can eventually leave the body.

“We’ve described these things separately, but from a biological perspective, they are almost certainly linked,” Iliff said.

Iliff said many of the new findings in mice still need to be confirmed in humans.

“The anatomical differences between rodents and humans are substantial,” he says.

But the results are consistent with research into the causes of neurodegenerative diseases like Alzheimer’s, he says.

Researchers know that the brain’s waste-clearing system can be impaired by aging, injury or disease that clogs the brain’s blood vessels.

“These are all risk factors for Alzheimer’s disease,” Iliff says.

Iliff says that impaired waste removal can contribute to Parkinson’s disease, headaches, and even depression, so finding ways to help the brain cleanse itself (by inducing slow electrical waves, for example) could prevent a range of ailments.