The brain's drain: How our brains flush out their waste and toxins

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The brain's drain: How our brains flush out their waste and toxins

How does the brain clean itself up? We now know a major way to eliminate toxins from the brain, and this discovery could help us understand what is wrong with age-related diseases, such as Alzheimer's disease.

The ways in which the brain eliminates waste
The location of cerebrospinal fluid in the brain is a long-standing mystery, says Gou Young Koh of the Korean Higher Institute of Science and Technology in South Korea.

In 2014, researchers have a network of vessels called meningeal lymphatic vessels located in the outer cerebral membrane that has been shown to play a role in regulating brain fluids, thus eliminating excess protein that can accumulate in the brain. However, due to the complex structure of the brain, it was not clear where most of this drainage was located.

To determine the pathways through which the fluid flows, Koh and his colleagues injected a dye and quantum dots into the mouse cerebrospinal fluid and then marked the trace of its exit from the brain using brain scans.

They found that the basal meningeal lymphatic vessels allowed cerebrospinal fluid to enter and exit the brain at the base of the skull, but not at the top.

A significant age-related decrease
The team found a significant decrease in cerebrospinal fluid drainage in the brains of elderly mice. Animals aged 2 years or older had about half of the drainage through their basal meningeal lymphatic vessels compared to those aged 3 months.

"It's amazing that this is such a fundamental anatomical question and we don't know how to eliminate something important like a liquid around the brain," says Steven Proulx of the University of Bern in Switzerland.

But according to other researchers, drainage pathways in the nasal region and even in the optical region are as important, if not more important, than lymphatic vessels.

Toxic proteins
Drainage of cerebrospinal fluid is thought to be important for brain health. In conditions such as Alzheimer's disease, because proteins such as amyloids can accumulate in the brain and cause damage.

Proulx explains that the brain can have several ways to drain fluids, including the spine. "It is important to know where this flow occurs to understand the immune reactions that can occur in the central nervous system and how to eliminate toxic proteins such as amyloids.

He also suggests that it may be possible to use growth factors to stimulate brain drainage to treat neurodegenerative disorders.

Evidence that was not conclusive
Some research has previously suggested that toxins are mainly released from the brain during sleep, but other studies have shown that this evidence is inconclusive.