- The bacteria in our microbiota regulate our production of serotonin.
- Without them, our body cannot synthesize enough of it, which affects REM sleep, the most important phase.
- Serotonin is the hormone responsible for the circadian cycle that tells us when to sleep and when to stay awake.
Sleep is a complex process. Due to our rhythm of life, this phase, which is vital for our body, is often disrupted. During sleep, however, our organism regenerates, our memory fixes memories and we prepare ourselves for a new day. Researchers at Tsukuba University (Japan) have found that our sleep also depends on the bacteria and microorganisms in our digestive system as they regulate serotonin, which is necessary to maintain a good circadian cycle. Their results were published in the journal Scientific Reports November 11, 2020.
The interest of the microorganisms of our microbiota
To elucidate the phenomenon, the researchers gave mice antibiotics for four weeks. Knowing the role of antibiotics in our body’s defenses, they can also eliminate certain bacteria in our digestive tract, thus weakening the microbiota.
The researchers then compared the gut contents of mice that no longer harbored these microorganisms with those of control mice that were fed the same. During digestion, food is broken down and converted into metabolites, small molecules. “We found more than 200 metabolite differences between groups of mice. About 60 normal metabolites were absent in mice lacking these microorganisms, and some varied in amount, sometimes more, sometimes less, compared to those in control mice,” said Masashi Yanagisawa, a professor at Tsukuba University.
Once this observation was established, researchers sought to understand what these metabolites were used for. By analyzing the accumulation of all metabolites, they discovered that the biological pathways most affected by antibiotic treatment are those involved in neurotransmitter production. Thus, the tryptophan-serotonin pathway was almost blocked in microbiota-depleted mice. This suggests that without certain gut microorganisms, the mice could not produce serotonin from the tryptophan they ingested. Likewise, these mice lacked metabolites of vitamin B6, which speed up the production of serotonin and dopamine.
Serotonin, a sleep regulator
Finally, electroencephalograms were performed on mice to monitor their brain activity during sleep. REM sleep was more disrupted in microbiota-deficient rodents than in control mice. REM sleep was more common during the day and night, while non-REM sleep was more common during the day. In other words, mice without a healthy microbiota switched between sleeping and waking states more frequently than their conspecifics.
“We found that microbial degradation eliminates serotonin in the gut, and we know that brain serotonin levels can affect the sleep-wake cycle,” concluded Masashi Yanagisawa. Therefore, altering gut microbes through dietary changes may help people with sleep disorders.”