A group of scientists from universities in the United States and Denmark claim to have discovered a new structure in the brain unknown until now. The lymphatic subarachnoid membrane (SLYM) is a fourth meningeal layer of the brain, possibly associated with protection against neurological diseases such as Alzheimer’s and multiple sclerosis.
Until then, it was believed that the central nervous system was covered by three layers of meninges – the dura mater, arachnoid mater and pia mater. The new study, published in science magazine on Thursday (5/1), it shows the existence of a fourth meningeal layer.
brain protection
SLYM is a thin, delicate structure, just a few cells thick, lying beneath the arachnoid layer. It forms a rigid barrier that helps to control the flow of cerebrospinal fluid (CSF) in and around the brain and to separate “clean” from “dirty” CSF.
This function suggests a likely role played by SLYM in the glymphatic system, which requires a controlled flow and exchange of CSF while removing toxic proteins — associated with Alzheimer’s and other neurological diseases of the central nervous system — from the brain.
“The discovery of this structure provides us with a much greater appreciation of the sophisticated role that the CSF plays not only in transporting and removing waste from the brain, but also in supporting its immune defenses,” explains one of the study’s authors, Maiken Nedergaard, co-director from the Center for Translational Neuromedicine at the Universities of Rochester and Copenhagen.
The slym membrane is positioned between the arachnoid and pia materia layersUniversity of Copenhagen/ Publicity
SLYM 03University of Copenhagen/ Publicity
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SLYM also plays an important role in the brain’s defenses, as the central nervous system maintains its own native population of immune cells. Membrane integrity prevents entry of outside immune cells.
The study showed that higher concentrations of immune cells gather in the membrane during inflammation and aging. When SLYM is disrupted after traumatic brain injury, the disruption of CSF flow impairs the glymphatic system and allows non-central nervous system immune cells to enter the brain.
This suggests that diseases such as multiple sclerosis, central nervous system infections and Alzheimer’s may be triggered or exacerbated by abnormalities in SLYM function.
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