The human brain, a mysterious and complex organ, has long fascinated scientists and philosophers alike. Its functions, including thought, emotion, and behavior, are integral to our very being, yet much about it remains a mystery. From the structure and function of its billions of cells, to the mechanisms behind its remarkable capabilities, the study of the brain is an ongoing journey of discovery. And with each new discovery, we come one step closer to unlocking the secrets of this incredible organ.

As one of the notable new discoveries in brain science, researchers at the University of Rochester and the University of Copenhagen, has identified a previously unknown component of brain anatomy that acts as a protective barrier and platform for immune cells to monitor the brain for signs of infection and inflammation. They called this new component, Subarachnoid LYmphatic-like Membrane (SLYM).

Oh yeah, I understand how complicated this could be for someone new to neuroanatomy or neuroscience, so let us dissect it a bit for better understanding.

The word “subarachnoid” refers to the space between the arachnoid membrane and the pia mater, which are layers of tissue that cover the brain and spinal cord. The term “lymphatic-like” suggests that the membrane in question has some characteristics that are similar to lymphatic vessels or tissues. Lymphatic vessels and tissues are part of the lymphatic system, which is a network of vessels and organs that help to drain excess fluid, waste, and other substances from the body.

The traditional view is that the brain is surrounded by three layers, the dura, arachnoid, and pia mater. Møllgård et al. found a fourth meningeal layer called the subarachnoid lymphatic-like membrane (SLYM).

The newly discovered component is made up of thin and delicate cells called mesothelia, similar to what is found in other organs such as the lungs and heart, which typically forms a protective covering to organs, while also harbouring immune cells. This discovery stems from the idea of Møllgård, whose research focuses on developmental neurobiology and the systems of barriers that protect the brain. It was Møllgård who first suggested that a protective membrane similar to that in other parts of the body, might exist in the central nervous system as well.

The SLYM, although a very thin and delicate membrane consisting of only one or a few cells in thickness, acts as a tight barrier which allows only small molecules to pass through. This suggest that SLYM may play a significant role in the glymphatic system- controlling the flow and exchange of Cerebrospinal fluid (CSF) to allow for the influx of fresh CSF and the removal of toxic proteins associated with neurological diseases such as Alzheimer’s. The discovery will help researchers more precisely understand the mechanics of the glymphatic system, which was recently the subject of a $13 million grant from the National Institutes of Health’s BRAIN Initiative to the Center for Translational Neuromedicine at the University of Rochester.
In addition to its potential role in the glymphatic system, the SLYM also appears to be important for the brain’s immune defenses. The central nervous system has its own native population of immune cells, and the integrity of the SLYM prevents outside immune cells from entering the brain and potentially causing damage. The SLYM also allows immune cells within the brain to monitor for signs of infection and inflammation. This function is particularly important as the brain is particularly vulnerable to infection and inflammation due to its lack of lymphatic vessels, which are important for immune defense in the rest of the body.

The discovery of the SLYM is an exciting development in the field of neuroscience and has the potential to greatly improve our understanding of the brain and its functions. Further research on the SLYM and its role in the glymphatic system and immune defense will likely lead to new insights and potentially even new treatments for neurological diseases.
The SLYM was discovered through the use of advanced neuroimaging and molecular biology techniques. These tools have allowed scientists to study the living brain in unprecedented detail, leading to many important discoveries in the field of neuroscience. The team, led by Maiken Nedergaard, co-director of the Center for Translational Neuromedicine at University of Rochester and the University of Copenhagen, and Kjeld Møllgård, a professor of neuroanatomy at the University of Copenhagen, has previously made significant contributions to the understanding of the human brain, including detailing the functions of previously overlooked cells called glia and the discovery of the glymphatic system, the brain’s unique process of waste removal.
The team, as well as other scientists, will continue to study the SLYM, as it possess the potential to greatly improve our understanding of the brain and its functions, leading to new insights and even new treatments for neurological diseases.

Other Co-authors are: Felix Beinlich, Peter Kusk, Leo Miyakoshi, Christine Delle, Virginia Pla, Natalie Hauglund, Tina Esmail, Martin Rasmussen, Ryszard Gomolka, and Yuki Mori with Center for Translational Neuromedicine at the University of Copenhagen

Read the Original Research here: A mesothelium divides the subarachnoid space into functional compartments– Kjeld Møllgård et al. Science