Brain's 'Glymphatic' System Clears Interstitial Solutes

System may clear proteins implicated in neurodegenerative diseases
Brain's 'Glymphatic' System Clears Interstitial Solutes

THURSDAY, Aug. 16 (HealthDay News) -- Similar to the lymphatic system, the brain also contains a newly discovered system to drain waste, dubbed the "glymphatic" system, which may clear proteins implicated in neurodegenerative diseases, according to a study published in the Aug. 15 issue of Science Translational Medicine.

Noting that the brain lacks a lymphatic circulation, Jeffrey J. Iliff, Ph.D., from the University of Rochester Medical Center in New York, and colleagues used two-photon imaging with fluorescent tracers in live mice to understand how interstitial solutes from the brain interstitium move from the parenchyma to the cerebrospinal fluid (CSF).

The researchers found that CSF enters the parenchyma through a drainage system surrounding penetrating arteries and that brain interstitial fluid is cleared through a drainage system surrounding veins exiting the brain. Further experiments showed that the drainage system is formed through astroglial perivascular projections containing the aquaporin-4 water channel. Animals lacking this channel in astrocytes exhibited slowed CSF influx and a 70 percent reduction in clearance of interstitial solutes. Amyloid-β peptide, implicated in Alzheimer's disease, was transported through this system.

"We have identified a brain-wide pathway for fluid transport in mice, which includes the para-arterial influx of subarachnoid CSF into the brain interstitium, followed by the clearance of interstitial fluid along large-caliber draining veins," Iliff and colleagues conclude. "In light of its dependence on glial water flux, and its subservience of a lymphatic function in interstitial solute clearance, we propose that this system be called the 'glymphatic' pathway."

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