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I can't resist posting excerpts from a recent article announcing that researchers just found an entirely new lymph system ("lymphatic vessels") in the brain that transports fluid in the brain, and is probably "crucial to metabolic and inflammatory processes".  The image in this post shows the system in the brain. Amazing that it is only now "discovered" - apparently it was noticed by an anatomist 2 centuries ago, but this was pooh-poohed by modern day physicians. Until now. Excerpts from the Atlantic:

Scientists Somehow Just Discovered a New System of Vessels in Our Brains

You are now among the first people to see the brain’s lymphatic system. The vessels in the photo above transport fluid that is likely crucial to metabolic and inflammatory processes. Until now, no one knew for sure that they existed. Doctors practicing today have been taught that there are no lymphatic vessels inside the skull. Those deep-purple vessels were seen for the first time in images published this week by researchers at the U.S. National Institute of Neurological Disorders and Stroke.

In the rest of the body, the lymphatic system collects and drains the fluid that bathes our cells, in the process exporting their waste. It also serves as a conduit for immune cells, which go out into the body looking for adversaries and learning how to distinguish self from other, and then travel back to lymph nodes and organs through lymphatic vessels.

Senior investigator Daniel Reich trained as both a neurologist and radiologist, and his expertise is in inflammatory brain disease. The connection between the immune system and the brain is at the core of what he says he spends most of his time thinking about: multiple sclerosis. The immune system appears to modulate or even underlie many neurologic diseases, and the cells of the central nervous system produce waste that needs to be washed away just like other metabolically active cells. This discovery should make it possible to study how the brain does that, how it circulates white blood cells, and how these processes may go awry in diseases or play a role in aging.

Around the same time, researchers discovered fluid in the brains of mice and humans that would become known as the “glymphatic system.” It was described by a team at the University of Rochester in 2015 as not just the brain’s “waste-clearance system,” but as potentially helping fuel thebrain by transporting glucose, lipids, amino acids, and neurotransmitters.

Wouldn’t neurosurgeons, at some point in their meticulous down-to-the-millimeter dissecting of brains, have stopped and said, “Hey ... what’s this thing?”The lymph vessels probably escaped detection because they’re inside a thick membrane, the dura mater, which is the consistency of leather. They run alongside blood vessels that are much larger, and on MRI the signal that creates the images is dominated by the blood vessels.  

But this pathway appears crucial to life and health. A 2013 study in Science found that glymphatic flow seems to increase by almost double during sleep (in mice). Sleep disturbances are a common feature in Alzheimer’s and other neurologic disorders, and it’s possible that inadequate clearing of the brain’s waste products is related to exacerbating or even causing the disease.... 

The flow of glymphatic fluid can change based on a person’s intake of omega-3 fatty acids, a study showed earlier this year. Preliminary findings like these together suggest a pathway through which nutrition and sleep can be related to neurologic disorders. Optimizing this glymphatic flow could become a central theme for the future of neurologic health. “If all of this is true, there probably is a connection between these two systems, glymphatic and lymphatic,” Reich said. “And that would be one of the major functions of cerebrospinal fluid.”

From The Atlantic. Credit: Daniel Reich/ National Institute of Neurological Disorders and Stroke

Textbooks will have to be rewritten with the recent discovery of a system of lymphatic vessels that are a direct link from the immune system to the brain. Amazing that after centuries of studying people, that only now was this system detected (but they are very small and they follow a major blood vessel down into the sinuses). After extensive research,  the researchers determined that these vessels carry both fluid and immune cells from the cerobrospinal fluid, and that they exist in humans. The discovery reinforces findings that immune cells are present even within healthy brains, a notion that was doubted until recently.From Medical Daily:

Discovery Of 'Missing Link' Between Brain And Immune System Could Change How Disease Is Studied

The recent discovery of a "missing link" between the brain and the immune system may lead to a complete revision of biology textbooks. The link, vessels of the lymphatic system that run through the sinuses, were previously unidentified and thought not to exist. However, the true significance of the discovery lies in the potential effects this finding could have on both the study and treatment of neurological diseases such as Alzheimer’s disease and multiple sclerosis.  

The newly discovered "central nervous system lymphatic system vessels" follow a major blood vessel down into the sinuses, an area that has been traditionally difficult to obtain images of. Their presence is causing a stir in the medical world, as the researchers responsible believe the vessels may help to explain current medical mysteries, such as why patients with Alzheimer’s disease have accumulations of large protein plaques in the brain.

The fascinating discovery was made by researchers at the University of Virginia School of Medicine, and a study on the finding is currently available in the online journal Nature....Using a recently developed method, the team mounted the meninges, the membranes covering the brain, on a single slide so that they could be better observed. Only after doing this were they able to notice the brain’s elusive lymphatic vessels.   "It's so close to the blood vessel, you just miss it," Kipnis said. "If you don't know what you're after, you just miss it."

The team believes that the “missing link” between the brain and the immune system could explain why some diseases like Alzheimer’s can cause plaque buildup in the brain. Kipnis believes this plaque may be the result of the meningeal lymphatic vessels not efficiently removing buildup before it reaches the brain. Although scientists are currently not sure what causes cell death and tissue loss in the brains of those with Alzheimer’s, this plaque buildup is believed to play a role.

It’s not just the presence of plaque in the brain that the researchers hope this discovery can shed light on. According to Kipnis, this discovery could completely change the way we perceive the neuro-immune interaction.“We believe that for every neurological disease that has an immune component to it, these vessels may play a major role,” Kipnis said. “Hard to imagine that these vessels would not be involved in a [neurological] disease with an immune component.”The vessels also appear to look different with age, which has lead the researchers to suggest that they may play a role in the aging process.

Missing link found between brain, immune system -- with major disease implications Maps of the lymphatic system: old (left) and updated to reflect UVA's discovery.   Credit: University of Virginia Health System