Scientists just discovere a new protective layer of the brain

It is a membrane that acts as a “defence barrier”. The finding could be key to the future study of neurodegenerative diseases.

The human brain is a tremendously complex organ that does not reveal all its secrets. Thanks to advances in imaging technology, hidden forms and functions of neurological anatomy continue to emerge, from new types of nerve cells to entirely new tissue protrusions.

Now, researchers at the University of Copenhagen and the University of Rochester have identified a layer of tissue that helps protect our grey and white matter, one that has never been seen before.

Scientists just discovere a new protective layer of the brain

Only a few cells thick, this membrane appears to play a role in mediating the exchange of small, dissolved substances between compartments in the brain. It also appears to be the base of operations for the brain’s specific immune cells, not to mention aiding in the brain’s waste disposal (glyphatic) system.

University of Copenhagen molecular biologist Kjeld Møllgård and colleagues named their discovery the subarachnoid LYmphatic-like membrane (SLYM). They used two-photon microscopy for the finding.

The SLYM sits between two other membranes that protect the brain. It divides our brain fluid space in two, bringing the total number of known membranes enveloping our brain to four.

Scientists just discovere a new protective layer of the brain

Unlike the rest of our body, our central nervous system has no lymphatic (immune) vessels and is considered immune privileged, a term that refers to sites in our body where immune responses are highly controlled, such as our eyes and testicles.

The team therefore suspects that cerebrospinal fluid may capture some of the role of the immune system in the brain. The presence of SLYM could explain how this works.

“The discovery of a new anatomical structure that secretes and helps control. The flow of cerebrospinal fluid (CSF) in and around the brain now gives us a much greater appreciation of the sophisticated role. CSF plays not only in transporting and removing waste from the brain. But also in supporting its immune defences,” says University of Rochester neuroscientist Maiken Nedergaard.

SLYM is the mesothelium of the brain
The SLYM shares molecular markers with the mesothelial membrane that lines the rest of our organs, enclosing their blood vessels and storing immune cells. So the researchers propose that the SLYM is the mesothelium of the brain, which lines the blood vessels in the cavity between the brain and skull.

The mesothelium also plays the role of lubricant between organs that slide past each other.

“Physiological pulsations induced by the cardiovascular system, respiration and positional changes of the head are constantly shifting the brain within the cranial cavity,” the researchers explain in their paper. “SLYM can, like other mesothelial membranes, reduce the friction between the brain and the skull during such movements.”