New direct links discovered between the brain and its surrounding environment

Feb. 8, 2024
NIH collaboration has implications for neural-immune system responses and aging.

In a recent study of the brain’s waste drainage system, researchers from Washington University in St. Louis, collaborating with investigators at the National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institute of Health (NIH), discovered a direct connection between the brain and its tough protective covering, the dura mater.

These links may allow waste fluid to leave the brain while also exposing the brain to immune cells and other signals coming from the dura. This challenges the conventional wisdom which has suggested that the brain is cut off from its surroundings by a series of protective barriers, keeping it safe from dangerous chemicals and toxins lurking in the environment.

NINDS’s Daniel S. Reich, M.D., Ph.D.’s group worked jointly with the lab of Jonathan Kipnis, Ph.D., a professor at Washington University in St. Louis.

Reich’s lab used high-resolution magnetic resonance imaging (MRI) to observe the connection between the brain and body’s lymphatic systems in humans.

Using MRI, the researchers scanned the brains of a group of healthy volunteers who had received injections of gadobutrol, a magnetic dye used to visualize disruptions in the blood brain barrier or other kinds of blood vessel damage. Large veins are known to pass through the arachnoid barrier carrying blood away from the brain, and these were clearly observed on the MRI scans. As the scan progressed, a ring of dye appeared around those large veins that slowly spread out over time, suggesting that fluid could make its way through the space around those large veins where they pass through the arachnoid barrier on their way into the dura.     

Together, the labs found a “cuff” of cells that surround blood vessels as they pass through the arachnoid space. These areas, which they called arachnoid cuff exit (ACE) points, appear to act as areas where fluid, molecules, and even some cells can pass from the brain into the dura and vice versa, without allowing complete mixing of the two fluids. In some disorders like Alzheimer’s disease, impaired waste clearance can cause disease-causing proteins to build up.

Reich and his team also observed an interesting connection between the participants’ age and the leakiness of ACE points. In older participants, more dye leaked into the surrounding fluid and space around the blood vessels.

NIH release