Every day, as you move about in the world, your brain is chugging along with you. Just like any other engineer, or organ, as it works, millions of neurons firing and guiding you around, the brain builds up waste products. But for a long time it wasn't clear where that waste went. Now, scientists think they know the answer.
They're calling the draining pipes the "the glymphatic system" - after the glial cells that control it and the lymphatic system that it resembles. The system works like a series of pipes to funnel waste away from the brain. A new paper in Science Translational Medicine describes the system as they observed it in mice.
Researchers knew about a slower system to remove waste. A fluid called the cerebrospinal fluid (CSF) moves through the brain and carries away waste through diffusion. But this new system works much faster. Senior author on the paper Maiken Nedergaard describes how the system works in the press release:
"It's as if the brain has two garbage haulers – a slow one that we've known about, and a fast one that we've just met," said Nedergaard. "Given the high rate of metabolism in the brain, and its exquisite sensitivity, it's not surprising that its mechanisms to rid itself of waste are more specialized and extensive than previously realized."
But how was there an entire structure for draining in the brain, without us knowing about it? The press release explains:
The scientists say the system operates only when it's intact and operating in the living brain, making it very difficult to study for earlier scientists who could not directly visualize CSF flow in a live animal, and often had to study sections of brain tissue that had already died. To study the living, whole brain, the team used a technology known as two-photon microscopy, which allows scientists to look at the flow of blood, CSF and other substances in the brain of a living animal.
Knowing how the brain deals with waste is important for how we understand nutrient delivery and potential ways in which that waste removal system might break down and cause problems. Jeffrey Iliff, a research assistant in Nedergaard's lab explains, in the press release, how that might happen:
"If the glymphatic system fails to cleanse the brain as it is meant to, either as a consequence of normal aging, or in response to brain injury, waste may begin to accumulate in the brain. This may be what is happening with amyloid deposits in Alzheimer's disease," said Iliff. "Perhaps increasing the activity of the glymphatic system might help prevent amyloid deposition from building up or could offer a new way to clean out buildups of the material in established Alzheimer's disease," he added.