A mesothelium divides the subarachnoid space into functional compartments
The central nervous system is lined by meninges, classically known as dura, arachnoid, and pia mater. We show the existence of a fourth meningeal layer that compartmentalizes the subarachnoid space in the mouse and human brain, designated the subarachnoid lymphatic-like membrane (SLYM). SLYM is morpho- and immunophenotypically similar to the mesothelial membrane lining of peripheral organs and body cavities, and it encases blood vessels and harbors immune cells. Functionally, the close apposition of SLYM with the endothelial lining of the meningeal venous sinus permits direct exchange of small solutes between cerebrospinal fluid and venous blood, thus representing the mouse equivalent of the arachnoid granulations. The functional characterization of SLYM provides fundamental insights into brain immune barriers and fluid transport.
Left panel shows that SLYM (green) separates the subarachnoid space (SAS)into an upper and a lower compartment. Red microspheres (1 μm) were injected into theupper SAS and blue microspheres (1 μm) were injected into the lower SAS. SLYM preventedthe microspheres from mixing. The right panel shows a schematic drawing of SLYM and listswhich antigen SLYM and theclassicalmembranessurrounding the brain from it surroundingexpress. The list validates that SLYM by its antigen expressiondiffersfrom the3 well-knownmembranes, dura, arachnoid and pia,surrounding the brain.
“The discovery of a new anatomic structure that segregates and helps control the flow of cerebrospinal fluid (CSF) in and around the brain now provides us much greater appreciation of the sophisticated role that CSF plays not only in transporting and removing waste from the brain, but also in supporting its immune defenses.”
Prof. Dr. Maiken Nedergaard
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