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A problem with the glymphatic system could mean that amyloid is not being removed correctly

The brain has a waste removal process that could one day be used to better treat problems like Alzheimer's disease.

Researchers from the University of Rochester Medical Center (URMC) -- led by Maiken Nedergaard, M.D., D.M.Sc., co-director of the URMC Center for Translational Neuromedicine -- detailed a recently discovered waste removal system in the brain, and believes it could hold the key to understanding and treating diseases like Alzheimer's. 

It's been long understood that the lymphatic system, which is a circulatory network of vessels and organs, is responsible for waste removal throughout the body. However, it doesn't perform this task in the brain. Last August, URMC researchers discovered the glymphatic system, which filled in the missing piece as the brain's own "garbage truck."

The glymphatic system works like this: the brain is surrounded by the arachnoid membrane, which is covered in cerebral spinal fluid (CSF). CSF uses pathways that lead into the brain with the support of glia cells. These are the same pathways that arteries use to carry blood, creating a parallel system where CSF is carried through on an outer ring and blood is carried through the inner ring.

CSF is rushed through the brain quickly, carrying waste such as excess proteins along with it as it sweeps through. This waste is then sent off into a similar system that parallels veins, and it travels down the spine until it is transferred to the lymphatic system. From there, it goes to the liver and is broken down. 

Researchers didn't discover this system until just last year because it cannot be seen in brain tissue samples. Instead, the team had to use imaging technology called two-photon microscopy. This allowed scientists to look within the brains of mice, thus discovering the glymphatic system. 

This study could help researchers find new ways to treat disorders like Alzheimer's disease because the disease is marked by the accumulation of the protein beta amyloid in the brain. A problem with the glymphatic system could mean that amyloid is not being removed correctly. 

This study was published in Science

Source: Science Daily



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By amanojaku on 6/28/2013 1:09:48 PM , Rating: 5
quote:
The glymphatic system works like this: the brain is surrounded by the arachnoid membrane, which is covered in cerebral spinal fluid (CSF). CSF uses pathways that lead into the brain with the support of glia cells. These are the same pathways that arteries use to carry blood, creating a parallel system where CSF is carried through on an outer ring and blood is carried through the inner ring.
The brain is covered in three protective meninges (membranes): the pia mater (in contact with the brain), the arachnoid membrane, and the dura mater (in contact with the skull).

CSF is found in the subarachnoid space, BELOW the arachnoid membrane and ABOVE the pia mater. The arachnoid membrane is not covered in CSF; rather, it contains CSF.

Glial cells (or simply "glia"), specifically ependymal cells, create CSF from blood. CSF is essentially filtered blood plasma with no blood cells and extremely low concentrations of solutes. These ependymal cells are found in the choroid plexus of the brain, and are part of the blood-brain barrier that protects the brain from disease. CSF travels through the brain using the glymphatic system.

The glymphatic (glial lymphatic) system pathways are known as paravascular spaces or perivascular spaces. They are simply openings around arteries and veins (the blood vessels) that penetrate the brain. They are functionally similar to the vessels, but structurally different. Where the vessels are made up of up to three layers (tunica interna or intima - smooth layer; tunica media - muscle layer; and tunica externa - anchoring layer), the vascular spaces are NOT layered. They are lined with astrocytes, another type of glial cell that plays a role in the blood-brain-barrier.

Not much is known about the glymphatic system since it was only discovered last year. There is a lack of information on astrocytes, as well. Scientists have redefined the functions of astrocytes a few times as scanning technology improves. It is thought that astrocytes are similar to garbage men, and that the CSF is like a conveyor belt for garbage. A poorly functioning glymphatic system is implicated in neurological diseases such as ALS, Parkinson's, etc... because of the presence of extracellular protein plaques.

"A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid ß."
http://www.ncbi.nlm.nih.gov/pubmed/22896675

"Brain-wide pathway for waste clearance captured by contrast-enhanced MRI"
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC358215...




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