With the fall and winter holidays approaching, many will be thinking about the relationship between eating and sleeping. Researchers led by Professor Masashi Yanagisawa of the University of Tsukuba in Japan hope they can focus people on the key intermediates in the equation: bacterial microbes in the gut. Their detailed study in mice revealed the extent to which bacteria can alter the environment and contents of the intestines, ultimately affecting behaviors such as sleep.
The experiment itself was quite simple. The researchers gave a group of mice a powerful cocktail of antibiotics for four weeks, so that they no longer had any gut microorganisms. They then compared gut contents between these mice and control mice that had the same diet. Digestion breaks food down into bits and pieces called metabolites. The research team found significant differences between metabolites in the microbiota-depleted mice and the control mice. As Professor Yanagisawa explains, “we found over 200 metabolite differences between mouse groups. About 60 normal metabolites were missing in the microbiota-depleted mice, and the others differed in number, some more and some less than in the control mice.”
The team then set out to find out what these metabolites normally do. Using enrichment analysis of metabolome sets, they found that the biological pathways most affected by antibiotic treatment were those involved in making neurotransmitters, the molecules that cells in the brain use to communicate with each other. Thus, the tryptophan-serotonin pathway was almost completely shut down; the microbiota-depleted mice had more tryptophan than the controls, but almost zero serotonin. This shows that without significant gut microbes, the mice could not make serotonin from the tryptophan they ate. The team also found that the mice were deficient in vitamin B6 metabolites, which accelerate the production of the neurotransmitters serotonin and dopamine.
The team also analyzed how the mice slept by looking at brain activity in EEGs. They found that compared to the control mice, the microbiota-depleted mice had more REM and non-REM sleep at night – when mice should be active – and less non-REM sleep during the day – when mice should. must be. usually sleep. The number of REM sleep episodes was higher both during the day and at night, while the number of non-REM episodes was higher during the day. In other words, the microbiota deficient mice switched between sleep / wake stages more often than the controls.
Professor Yanagisawa speculates that serotonin deficiency was responsible for the sleep abnormalities; however, the exact mechanism remains to be worked out. “We found that the depletion of microbes eliminated serotonin in the gut, and we know that serotonin levels in the brain can affect sleep / wake cycles,” he says. “So changing the microbes in the gut by changing the diet can help people who have trouble sleeping.”
So, this holiday season, if you feel sleepy after eating tryptophan-filled turkey, don’t forget to thank your gut microbes!
Material provided by University of Tsukuba. Note: Content can be edited for style and length.