
Tracking fluid flow in mouse brains revealed that norepinephrine drives cleansing in non-REM sleep. Photo Credit: Adrian Eugen Ciobaniuc
Health USALooks Like Sleeping <em>Cleans</em> the Brain!
Through a recent study on mice, scientists affiliated with the University of Rochester, the United States, further their knowledge of the brain and its capacity to flush out chemical waste during sleep.
“Because the skull boxes in the brain, the contraction and relaxation of blood vessels create a pump that circulates the cerebrospinal fluid,” explains neuroscientist Maiken Nedergaard, lead author of the study. “When the vessels clench after a pulse of norepinephrine, cerebrospinal fluid moves in to fill the gap. And when the blood vessels relax, they push the cerebrospinal fluid along.”
In 2012, scientists identified an alternative drainage system that allows cerebrospinal fluid — the liquid in which the brain bathes — to circulate via tiny passages alongside blood vessels. The flow also accelerates during sleep. Through the latest mice study, the team wanted to identify what keeps the cerebrospinal fluid moving along the brain. It was observed that when mice were in non-REM sleep, during which the body’s tissues undergo renewal, blood volume in the brain oscillated, and norepinephrine levels varied. The neurotransmitter norepinephrine might not be the only player, but “we have identified maybe the most important driver of glymphatic flow in non-REM sleep.” Humans, like mice, show oscillations in norepinephrine release and blood vessel pulsations during sleep. Therefore, the exact pumping mechanism could be operating in human brains.