By John Hammon
As of last Thursday, January 5th 2023, Researchers at the University of Rochester and the University of Copenhagen announced the discovery of a previously unknown layer of tissue inside the brain that exists inside both human and mouse brains. The layer of tissue has been dubbed as the Subarachnoidal Lymphatic-like Membrane, or SLYM for short.
According to conclusive observations made by the researchers, the SLYM primarily serves as a protective barrier for the brain. While also providing a platform for immune cells to look for things like infection and inflammation inside the brain. It simultaneously reduces friction between the brain and skull as the brain moves around inside the cranium. This guides the flow of the cerebrospinal fluid, which is a clear liquid that bathes the outside of the brain. The SLYM’s position also divides the subarachnoid space, which is the region that contains the cerebrospinal fluid surrounding the brain. The division of the subarachnoid spaces consists of two parts.
Researchers inside the labs of Maiken Nedergaard, the co-director of the Center for Translational Neuromedicine, and Kjeld Møllgård, a professor of neuroanatomy, discovered the SLYM using complex high resolution two-photon excitation microscopy, along with fluorescent protein dyes. After Identification of the structure, the researchers conducted various experiments on mice to determine its exact function. In short, they tested to explore what could cross the SLYM and what couldn’t. They also noticed that the SLYM hosts its own population of nervous system immune cells that is comparable to the mesothelial tissue, which is a thin protective layer that surrounds other vital organs.
The researchers also theorized that the SLYM had another function, which again plays a part with the cerebrospinal fluid. The running theory is that because of other recent discoveries about the cerebrospinal fluid that pointed to the fluid as a medium for clearing waste products that build up in our brains while we are awake, the SLYM might be the driving force behind pumping clean cerebrospinal fluid, and draining dirty cerebrospinal fluid. Maiken Nedergaard was said to have stated this in a statement. “The discovery… provides us much greater appreciation of the sophisticated role that cerebrospinal fluid plays not only in transporting and removing waste from the brain, but also in supporting its immune defenses.”
Researchers also say that the new discovery of the SLYM also tells us more about brain trauma. For example one researcher was said to have stated this: “Physical rupture of the SLYM could, by altering cerebrospinal fluid flow patterns, explain the prolonged suppression of glymphatic flow after traumatic brain injury as well as the heightened posttraumatic risk of developing Alzheimer’s disease.” This basically translates to the connection that damage to the SLYM could be the main cause for maybe central nervous system disorders. It is also worth noting that going forward, scientists exploring novel brain therapeutics may have to take the SLYM into account when designing certain therapies, otherwise there could be major consequences.
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