Glowing Mouse Heads and How Our Brains Get Washed

Herewith, edited excerpts from a Washington Post article of special interest to people with brains:

The lymph network carries immune cells throughout the body and removes waste and toxins. It was accepted wisdom for more than 300 years that the network didn’t extend into the brain. 

Three years ago, scientists trying to develop a more precise map of the lymphatic system used genetically-modified mice whose lymphatic vessels glowed when illuminated by a particular wavelength of light. The mice had been given a gene from a species of glowing jellyfish.

Seeing that the mouse’s heads glowed, the researchers realized that the lymphatic vessels extended into the brain after all. This was surprising, to say the least: In the 21st century, major findings involving basic human anatomy are rare. “These days, you don’t make discoveries like this”, one of the scientists said.

Since the lymph network also extends into human brains, this discovery has major implications for a wide variety of brain diseases, including Alzheimer’s, multiple sclerosis, stroke and traumatic brain injury.

Researchers have identified two networks: the vessels that lead into and surround the brain, and those within the brain itself. The latter is called the “glymphatic” system for the glia, the kind of neuron that makes up the lymphatic vessels in the brain. The glymphatic vessels carry cerebrospinal fluid and immune cells into the brain and remove cellular trash from it.

There is evidence that when the systems malfunction, the brain can become clogged with toxins and suffused with inflammatory immune cells. Over decades, this process may play a key role in Alzheimer’s disease, Huntington’s disease, Parkinson’s disease and other degenerative illnesses. 

“This is a revolutionary finding,” one researcher says. “This system plays a huge role in the health of the brain.” She describes the glymphatic system as like a dishwasher for the brain. “The brain is very active and so it produces a lot of junk that needs to be cleaned out.”

In hindsight, the system should have been noticed long ago. When the skull and head are dissected, the vessels are visible to the naked eye. But no one bothered to really look.

The vessels have also been implicated in autoimmune disease, such as multiple sclerosis. Researchers knew that the immune system has limited access to the brain. But at the same time, the immune system kept tabs on the brain’s status; no one knew exactly how. Some researchers theorize that the glymphatic system could be the conduit. In diseases like multiple sclerosis — where the body’s immune system attacks certain brain cells — the communication may go awry.

Recently, Harvard University researchers reported that glymphatic flow is significantly decreased in the period just before a migraine. The intense pain in these headaches is caused largely by inflamed nerves in the tissue that surrounds the brain. The authors of the study theorize that faulty clearance of molecular waste from the brain could trigger inflammation in these pain fibers.

One key to glymphatic performance seems to be sleep. At least in mice, the system processes twice as much fluid during sleep as it does during wakefulness. It’s possible that sleep dysfunction may contribute to Alzheimer’s and perhaps other brain illnesses: “You only clean your brain when you’re sleeping. This is probably an important reason that we sleep. You need time off from consciousness to do the housekeeping”.

It also appears that sleep position is crucial. In an upright position — someone who is sitting or standing — waste is removed much less efficiently. Sleeping on your stomach is also not very effective; sleeping on your back is somewhat better, while lying on your side appears to produce the best results. The reason for these differences might be related to the mechanical engineering of the lymphatic vessels and valves; the healthiest approach may be to move periodically while you sleep.

Sleep is probably not the only way to improve glymphatic flow. Omega-3 fatty acids and deep breathing may also improve glymphatic functioning. 

Not being a scientist, I can’t evaluate these studies, but it makes sense that brains produce a lot of junk that needs to be cleaned out. (And you didn’t think the President would come up in this post.)