Sleep Health | Sleep Review
Researchers working with a team from the University of Tsukuba have found new evidence of brain refreshment that takes place during a particular phase of sleep: REM (Rapid Eye Movement) sleep, when people dream the most.
Previous studies used various methods to measure differences in brain blood flow between REM sleep, non-REM sleep, and wakefulness, with conflicting results. In their latest work, the team led by Tsukuba used a technique to directly visualize the movement of red blood cells in the brain capillaries (where nutrients and waste products are exchanged between brain cells and blood) of mice while they are awake and asleep.
“We used a dye to make the blood vessels of the brain visible under fluorescent light, using a technique known as two-photon microscopy,” the study’s lead author and Professor Yu Hayashi said in a press release. “In this way we were able to directly observe the red blood cells in the capillaries of the neocortex in non-anesthetized mice.”
The researchers also measured electrical activity in the brain to identify REM sleep, non-REM sleep, and wakefulness, and looked for differences in blood flow between these phases.
“We were surprised by the results,” says Hayashi. “During REM sleep, there was massive red blood cell flow through the brain capillaries, but no difference between non-REM sleep and being awake, showing that REM sleep is a unique state.”
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The research team then interrupted the mice’s sleep, resulting in “rebound” REM sleep – a stronger form of REM sleep to make up for the earlier interruption. Blood flow in the brain was further increased during rebound REM sleep, suggesting a relationship between blood flow and REM sleep strength. However, when the researchers repeated the same experiments on mice lacking adenosine A2a receptors (the receptors that blockage makes you more alert after drinking coffee), there was less increase in blood flow during REM sleep, even during rebound. REM sleep.
“These results suggest that adenosine A2a receptors may be responsible for at least some of the changes in blood flow in the brain during REM sleep,” says Hayashi.
Given that decreased blood flow to the brain and decreased REM sleep are correlated with the development of Alzheimer’s disease, which involves the accumulation of waste products in the brain, it might be interesting to investigate whether there is increased blood flow to the brain capillaries during REM sleep is important for clearing waste from the brain. This study lays the groundwork for future research into the role of adenosine A2a receptors in this process, which could ultimately lead to the development of new treatments such as Alzheimer’s disease.
The study is published in Cell Reports.
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