Nedergaard’s team has dubbed the new system “the glymphatic system,” since it acts much like the lymphatic system but is managed by brain cells known as glial cells.
…Scientists have known that cerebrospinal fluid or CSF plays an important role cleansing brain tissue, carrying away waste products and carrying nutrients to brain tissue through a process known as diffusion.
The newly discovered system circulates CSF to every corner of the brain much more efficiently, through what scientists call bulk flow or convection.
…“Given the high rate of metabolism in the brain, and its exquisite sensitivity, it’s not surprising that its mechanisms to rid itself of waste are more specialized and extensive than previously realized.”
While the previously discovered system works more like a trickle, percolating CSF through brain tissue, the new system is under pressure, pushing large volumes of CSF through the brain each day to carry waste away more forcefully. The glymphatic system is like a layer of piping that surrounds the brain’s existing blood vessels.
…The team found that CSF is pumped into the brain along the channels that surround arteries, then washes through brain tissue before collecting in channels around veins and draining from the brain.
How has this system eluded the notice of scientists up to now? The scientists say the system operates only when it’s intact and operating in the living brain, making it very difficult to study for earlier scientists who could not directly visualize CSF flow in a live animal, and often had to study sections of brain tissue that had already died.
To study the living, whole brain, the team used a technology known as two-photon microscopy, which allows scientists to look at the flow of blood, CSF and other substances in the brain of a living animal.
…“It’s a hydraulic system,” said Nedergaard. “Once you open it, you break the connections, and it cannot be studied. We are lucky enough to have technology now that allows us to study the system intact, to see it in operation.”