TSUKUBA, Japan — New evidence of brain refreshing during a specific phase of sleep, i.e., rapid eye movement, has been found by a team from the University of Tsukuba in Japan. The rapid eye movement sleep happens when a person tends to dream a lot.
“Across multiple cortical areas, average capillary cerebral blood flow is largely increased during rapid eye movement sleep, whereas it does not differ between periods of active wakefulness and non-rapid eye movement sleep,” states the study.
Previous studies have measured differences in blood flow in the brain between rapid eye movement sleep, non-rapid eye movement sleep, and wakefulness using various methods, with conflicting results.
In their latest work, the Tsukuba-led team 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 during awake visualize red blood cells’ movement asleep states.
“We used a dye to make the brain blood vessels visible under fluorescent light, using a technique known as two-photon microscopy,” said senior author of the study Professor Yu Hayashi.
“In this way, we could directly observe the red blood cells in capillaries of the neocortex in non-anesthetized mice.”
The researchers also measured electrical activity in the brain to identify rapid eye movement sleep, non-rapid eye movement sleep, and wakefulness and looked for differences in blood flow between these phases.
“We were surprised by the results. There was a massive flow of red blood cells through the brain capillaries during rapid eye movement sleep,” said Hayashi.
“Still, no difference between non-rapid eye movement sleep and the awake state, showing that rapid eye movement sleep is a unique state.”
The research team then disrupted the mice’s sleep, resulting in “rebound” rapid eye movement sleep, a stronger form of rapid eye movement sleep to compensate for the earlier disruption.
Blood flow in the brain was further increased during rebound rapid eye movement sleep, suggesting an association between blood flow and quick eye movement sleep strength.
However, the researchers repeated the same experiments in mice without adenosine—an autacoid present in all tissue and body fluids — A2a receptors (the receptors whose blockade makes one feel more awake after drinking coffee), there was less of an increase in blood flow during rapid eye movement sleep, even during rebound rapid eye movement sleep.
“These results suggest that adenosine A2a receptors may be responsible for at least some changes in blood flow in the brain during rapid eye movement sleep,” said Hayashi.
Given that reduced blood flow in the brain and decreased rapid eye movement sleep are correlated with the development of Alzheimer’s disease, which involves the buildup of waste products in the brain, it may be interesting to address whether increased blood flow in the brain capillaries during rapid eye movement sleep is important for waste removal from the brain.
This study lays the preliminary groundwork for future investigations into the role of adenosine A2a receptors in this process, which could ultimately lead to new treatments for conditions such as Alzheimer’s disease.
(With inputs from ANI)
Edited by Saptak Datta and Ritaban Misra
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