THE ESSENTIAL
- The brain is surrounded by three meninges: the dura mater, the arachnoid mater and the pia mater.
- The SLYM disintegrates when the brain is removed during an autopsy.
She had gone completely unnoticed so far. Recently, scientists from the University of Copenhagen (Denmark) accidentally spotted a thin membrane that envelops the brain. This fourth meninge, called the “subarachnoid lymphatic-like membrane (SLYM)”, was described in the journal Science. In a statementthe researchers indicated that this “unknown component of brain anatomy served as a protective barrier“.
Brain: SLYM was first identified in mice
To arrive at this discovery, the team first examined the brains of mice. Then they quickly identified this thin membrane in the brains of human beings. According to the authors, the SLYM is a type of membrane called the “mesothelium” that lines other organs in the body, including the lungs and heart, and houses immune cells. In the brain, this thin membrane allows immune cells to detect infections and inflammation.
Lymphatic system: a filter of waste present in the brain
According to the scientists, this new membrane is very thin and is only one or a few cells thick. That’s why she’s invisible to brain scans. SLYM is believed to play a role in the lymphatic system allowing the influx of “fresh” cerebrospinal fluid (CSF) while removing toxic proteins associated with Alzheimer’s disease and other neurological conditions from the central nervous system.
Neurological diseases: abnormalities of SLYM function involved?
“The discovery of SLYM paves the way for further study of its role in brain disease. For example, the researchers note that greater and more diverse concentrations of immune cells accumulate on the membrane during inflammation and aging. When the membrane was ruptured during a traumatic brain injury, the disruption of CSF outflow impaired the lymphatic system and allowed immune cells from the non-central nervous system to enter the brain.” can we read in a press release.
These observations suggest that pathologies as diverse as multiple sclerosis, central nervous system infections and Alzheimer’s disease might be triggered or aggravated by abnormalities in SLYM function. According to the team, these results also suggest that the delivery of drugs and gene therapies to the brain might be affected by SLYM function, “what will need to be taken into consideration as new biological therapies are developed”.