A common sleep medication prevents mice from effectively clearing away waste and toxins from their brain during sleep
By Grace Wade
8 January 2025
During sleep, the brain flushes out toxins that accumulate throughout the day
Robert Reader/Getty Images
Sleeping pills might help you doze off, but the sleep you get may not be as restorative. When mice were given zolpidem, a medication commonly found in sleeping pills such as Ambien, it prevented their brains from effectively clearing waste during sleep.
Sleep is critical for removing waste from the brain. At night, a clear liquid called cerebrospinal fluid circulates around brain tissues, flushing out toxins through a series of thin tubes known as the glymphatic system. Think of it like a dishwasher that the brain turns on when asleep, says Maiken Nedergaard at the University of Rochester Medical Center in New York. However, the mechanism that pushes fluid through this network wasn’t well understood – until now.
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Nedergaard and her colleagues implanted optical fibres in the brains of seven mice. By illuminating chemical compounds in the brain, the fibres let them track the flow of blood and cerebrospinal fluid during sleep.
They found that as levels of a molecule called norepinephrine (also called noradrenaline) rise, blood vessels in the brain constrict, decreasing the volume of blood and allowing cerebrospinal fluid to rush into the brain. When norepinephrine levels fall, blood vessels expand, pushing cerebrospinal fluid back out. In this way, fluctuations in norepinephrine during non-rapid eye movement (NREM) sleep stimulate blood vessels to act like a pump for the glymphatic system, says Nedergaard.
This finding reveals that norepinephrine plays a crucial role in cleaning waste out of the brain. Previous research has shown that, as we sleep, our brains release norepinephrine in a slow, oscillating pattern. These norepinephrine waves occur during NREM, which is a crucial sleep stage for memory, learning and other cognitive functions.