Scientists, studying the brain, have found that blood flow in the brain capillaries, a process necessary for important for oxygen/nutrient delivery and waste removal, rises with during rapid eye movement sleep. This has been observed using rodents.
Rapid eye movement (begins, for a human, 90 minutes after a person falls asleep. Here brain activity increases, and the eyes dart around quickly, followed by an increase with the pulse, blood pressure, and breathing. This stage is when a person experiences most of their dreaming.
This suggests that adenosine A2a receptors are responsible for this increased blood flow. These are the receptors whose blockade makes a person feel more awake after drinking coffee.
The significance of this is not only with understanding sleep but with developing treatments for neurodegenerative diseases. This includes diseases thought to be the result of the consequence of a build-up of waste products in the brain, including Alzheimer’s disease.
To examine the effects, the research team used a dye to make the brain blood vessels visible under fluorescent light, and visualizing this through two-photon microscopy, which is a fluorescence imaging technique that allows imaging of living tissue up to about one millimeter in thickness.
At a later stage in the study, the research team proceeded to disrupt the mice’s sleep, causing a “rebound” REM sleep. This is a stronger form of REM sleep that led to the blood flow in the brain increasing further. This suggests an association between blood flow and REM sleep strength.
When the researchers repeated the same experiments in mice without adenosine A2a receptors, there was a lower increase in blood flow during REM sleep. Hence, the research conclusion that adenosine A2a receptors are responsible for blood brain flow regulation.
The next stage of the research is to assess whether increasing the blood flow in the brain capillaries during sleep is an important process for waste removal from the brain. Central to this is examining the role of adenosine A2a receptors in this process. This may lead to novel treatments for conditions like Alzheimer’s disease.
The research findings appear in the journal Cell Reports, with the study titled “Cerebral capillary blood flow upsurge during REM sleep is mediated by A2a receptors.”