There appears to be a scratch in the paint on the wall of the living room. How long has that been there? It cannot have just suddenly popped up because it is so high along the wall that nothing would even touch it. It likely has been there since the very painting of the room itself. So, how is it possible that it is just being noticed now, many years later? Looking closer, it appears to reveal an extremely intricate mosaic from the 1800s when the house was originally built. Sudden discoveries such as this are much more common than they seem and happen to everyone, including scientists, such as when scientists discovered the Subarachnoid Lymphatic-like membrane.
At the beginning of 2023, a new membrane of the brain was discovered through the use of high-resolution two-photon excitation microscopy. This new membrane is known as the Subarachnoid Lymphatic-like membrane, or the SLYM for short. The previously known membranes of the brain include the innermost layer, known as the pia mater, the next layer, known as the arachnoid layer, and the outermost membrane of the brain known as the dura matter.
This membrane went undiscovered for a variety of reasons. First, scientists had no reason to suspect an additional membrane was located here. It lies between the arachnoid and the pia mater layers, in an area known as the subarachnoid space. This space is filled with blood vessels, clear fluid known as cerebrospinal fluid (CSF), and connective tissue, so it seems to be just a space for these important components to function. Moreover, this membrane is as thin as one cell in certain locations, so the older microscopy, imaging, and experimental techniques were not powerful enough to identify the membrane.
This membrane explains many previously misunderstood mechanisms for how new cerebrospinal fluid is circulated throughout the brain and around arteries (periarterial influx). The SLYM membrane aids in facilitating a unidirectional movement of the cerebrospinal fluid throughout the brain. This flow helps to aid in the movement of molecules to the brain and the removal of waste from the brain to allow it to function at its highest capacity.
The SLYM also creates a strong barrier that prevents anything (solutes, pathogens, and more) larger than 3 kilodaltons from passing through. As such, this membrane serves to bolster the immune defense of the brain by functioning as an immune response monitor. The SLYM was observed to contain large numbers of myeloid cells such as macrophages and white blood cells. These myeloid cells increase in quantity during times of inflammation, aging, and other risk factors. These immune functions suggest that the SLYM plays a crucial role in maintaining the health of the brain.
This membrane may serve as the key to issues that have eluded explanation for a long time. For example, this membrane appears to resist Alzheimer’s disease by removing wastes such as beta-amyloid and tau to cleanse the brain. As such, the SLYM has many positive implications for research and treatment of neurological diseases such as Alzheimer’s, Parkinson’s Disease, dementia, in addition to a variety of neuropsychological conditions.
The SLYM also serves as a potential new method of treatment and drug administration due to its direct influence on the brain and its ability to circulate cerebrospinal fluid. Moreover, this membrane serves as a potential new avenue to learn more about another system: the glymphatic system. The glymphatic system is a waste-clearing system for the central nervous system. The exploration of the SLYM as well as the glymphatic system may open new therapeutic treatment avenues for a wide variety of neurological conditions. Further research of the SLYM membrane is being supported with a 13-million-dollar grant from the National Institute of Health (NHIH).
So, the next time something appears out of nowhere, seeming out of thin air, whether it be a tiny scratch in the paint or an odd line of cells forming a membrane, it may be a great idea to explore it further. There is no end to the number of possibilities that arise from exploring the tiniest inconsistency to the most glaring issue. Who knows, maybe the discovery could be just what the world needs to solve an extremely important issue.
Sources:
Charuchandra, S. (2023, January 27). Scientists discover a new protective layer in the brain. Advanced Science News. https://www.advancedsciencenews.com/scientists-discover-a-new-protective-layer-in-the-brain/
Mollgard, K., Nedergaard, M., Mori, Y., Gomolka, R. S., Rasmussen, M. K., Es-Mail, T., Hauglund, N. L., Plá, V., Delle, C., Miyakoshi, L. M., Kusk, P., & Beinlich, F. R. M. (2023, January 5). A mesothelium divides the subarachnoid space into … Science.org. https://www.science.org/doi/10.1126/science.adc8810
The newly discovered SLYM membrane was brain’s best kept secret until now. Psychiatrist.com. (2023, January 27). https://www.psychiatrist.com/news/newly-discovered-slym-membrane-was-brains-best-kept-secret-until-now/
Plá, V., Bitsika, S., Giannetto, M.J. et al. Structural characterization of SLYM—a 4th meningeal membrane. Fluids Barriers CNS 20, 93 (2023). https://doi.org/10.1186/s12987-023-00500-w
King Lab at Creighton University 