New 'Brain-Cleaning' System Discovered in Mice
WEDNESDAY, Aug. 15 -- The brain has a cleaning system that drains away waste products, a new study involving mice suggests.
Using advanced imaging technology, researchers from the University of Rochester Medical Center in New York found this previously unrecognized "glymphatic system," which they said functions in the brain under the direction of glial cells, similar to the body's lymphatic system. The researchers suggest their findings could lead to improved treatments for neurological conditions, such as Alzheimer's disease, stroke and Parkinson's disease.
Scientists note, however, that research with animals often fails to provide similar results in humans.
"Waste clearance is of central importance to every organ, and there have been long-standing questions about how the brain gets rid of its waste," senior study author Dr. Maiken Nedergaard, co-director of the university's Center for Translational Neuromedicine, said in a school news release. "This work shows that the brain is cleansing itself in a more organized way and on a much larger scale than has been realized previously."
The study was published online Aug. 15 in the journal Science Translational Medicine.
The newly discovered system moves cerebrospinal fluid, which cleanses brain tissue, throughout the brain more efficiently than previously thought, the researchers said. Under pressure, the system pushes large volumes of the fluid through the brain to remove waste forcefully.
"It's as if the brain has two garbage haulers -- a slow one that we've known about, and a fast one that we've just met," Nedergaard said. "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."
Pumped into the brain along channels surrounding arteries, cerebrospinal fluid washes through brain tissue before collecting in channels around veins and draining from the brain, the researchers explained.
They said the system was previously undetected because it operates only in living brains. Development of two-photon microscopy has now enabled scientists to study the brain of a living animal.
"It's a hydraulic system," Nedergaard said. "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."
The researchers specifically examined amyloid beta, the protein that accumulates in the brain of patients with Alzheimer's disease. More than half of the amyloid removed from the brain of a mouse was drained through the glymphatic system, they found.
"Understanding how the brain copes with waste is critical. In every organ, waste clearance is as basic an issue as how nutrients are delivered," Jeffrey Iliff, the study's first author and a research assistant professor at the University of Rochester Medical Center, said in the news release. "In the brain, it's an especially interesting subject because in essentially all neurodegenerative diseases, including Alzheimer's disease, protein waste accumulates and eventually suffocates and kills the neuronal network of the brain."
If the brain's cleansing system doesn't function properly, due to disease, injury or aging, waste may begin to accumulate in the brain, the researchers said.
"This may be what is happening with amyloid deposits in Alzheimer's disease," Iliff said. "Perhaps increasing the activity of the glymphatic system might help prevent amyloid deposition from building up, or could offer a new way to clean out buildups of the material in established Alzheimer's disease."
The U.S. National Institutes of Health has more about the brain and how it works.
Posted: August 2012
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