Alzheimer's - Dementia, Author Interviews, Sleep Disorders / 08.08.2015
Brain Waste Removal System Works Best While Sleeping on Side
MedicalResearch.com Interview with:
Helene Benveniste, MD, PhD
Professor of Anesthesiology and Radiology
Vice Chair for Research, Department of Anesthesiology
Stony Brook Medicine, Stony Brook NY
Medical Research: What is the background for this study?
Dr. Benveniste: The ‘glymphatic’ pathway is a part of the brain and is responsible for removal of waste products and excess fluid that built up especially during wakefulness. The concept was introduced by Nedergaard’s team in 2012 from University of Rochester. Importantly it has been shown to remove waste products such as soluble amyloid beta and tau protein which build up excessively in the brain of subjects afflicted with Alzheimer’s disease. The glymphatic system has been studied in detail in animal models (not yet humans) and actually is a brain-wide pathway which runs along (i.e. on the outside) of all vessels in the brain and connects to the space around the brain cells (referred to as the interstitial fluid (ISF) space). The outer part of the glymphatic network ‘tube’ is bordered by a certain type of brain cells so-called ‘astroglial’ cells which are arranged in a special way so that their endfeet cover >97% of the surface of all brain vessels. One can think of this as if the astroglial cell’s ‘endfeet’ are arranged as a donut shaped tube around all the vessels. On the astroglial endfeet there are special water channels (aquaporin-4 water channels) which are critical for how efficiently the glymphatic system can get rid of waste because it allows water to move fast through the brain tissue so as to ‘flush’ waste products out efficiently. The small gap between the astroglial endfeet also act like a ‘sieve’ so that only waste products of a certain size can access the entire pathway. Cerebrospinal fluid (CSF) circulates into the glymphatic pathway from the surface of the brain along the arteries which dives directly from the surface into the deeper part of the brain; and ultimately enters the space around the brain cells; and sweeps through it and thereby mixes with the interstitial fluid of the brain which contains waste products. The CSF-ISF mix with the waste products is then flushed out on the other ‘side’ along the veins and ultimately ends up in lymph vessels in the body and then in the blood.
It has been shown that the glymphatic pathway removes brain waste more efficiently in a state of ‘unconsciousness’ e.g. sleep or anesthesia when compared to wakefulness. Given this intriguing finding i.e. that sleeps seems to affect the waste clearance from the brain we thought that the next to look at was sleeping positions. We did these studies in anesthetized rodents.
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