The New York Times published an article on Saturday, January 11 about UR Medical Center’s new findings on how sleep clears away toxins in the brain.
This research was funded by the National Institute of Health. The principal investigator of the research and senior author of the resulting paper, Dr. Maiken Nedergaard, explained the study in a video posted on URMC’s website.
“When we are awake,” Nedergaard said, “the brain cells are working very hard at processing all the information about our surroundings whereas during sleep, [they] work very, very hard on removing all the waste…”
“The study took approximately three years,” Dr. Lulu Xie, who conducted many of the experiments, said.
Additional co-authors of the paper include Hongyi Kang, Qiwu Xu, Michael J. Chen, Yonghong Liao, Meenakshisundaram Thiyagarajan, John O’Donnell, Daniel J. Christensen, Charles Nicholson, Jeffrey J. Iliff, Takahiro Takano and Rashid Deane.
Nedergaard said that the study was based on research done a few years ago that highlighted the importance of cerebral spinal fluid (CSF) in the brain’s waste-management.
The new research paper, titled “Sleep Drives Metabolite Clearance from the Adult Brain,” shows that the glymphatic system–a waste removal system exclusive to the brain which contains CSF–is especially active during sleep.
“In the sleeping mice, we found the CSF flushing into the brain very quickly and broadly but in the awake brain, the CSF is just barely flowing,”  Xie said.
To find out the reason behind the increased flow of CSF, scientists in Nedergaard’s lab injected fluorescent dyes into the CSF of mice, producing another significant discovery.
“Surprisingly, we found that the spaces between [certain brain] cells increased around 60 percent from awake state to sleep state,” Xie said.
It is only recently that key findings have been made regarding the basic function of sleep. What then are the conditions that made it possible to produce Nedergaard’s findings?
“We have used microscopes that you can never, ever consider using in a clinic,” Nedergaard said.
Using two-photon microscopy, scientists can finally observe in detail the waste removal process in a living brain.
“The importance of all of this comes in developing a diagnostic test where we can predict which patient, prior to disease, might develop an accumulation of waste product,” Nedergaard explained.
This test is especially relevant to the diagnosis of neurodegenerative diseases, such as Alzheimer’s Disease, because of their association with the buildup of cellular waste products.
The research takes a step closer to finding ways to predict, prevent and treat these diseases by understanding how the glymphatic system regulates the amount of waste products.

Zeng is a member of  the class of 2017.

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