We commonly associate the gut with digestion and the absorption of nutrients, but research is showing that our gut may actually play an important role in sleep. Sleep has been shown to be extremely important in a variety of brain functions and is crucial in maintaining our physiological homeostasis. Our gut microbiota is heavily affected by the foods we consume and when we consume them. These foods are broken down into metabolites and can cause fluctuations in the status of our gut microbiota. Dysbiosis of our gut microbiota (a microbial imbalance in our gut), can impair a variety of our brain functions such as memory formation, mental health, and our sleep (causing issues such as insomnia). Studies in regard to the role of our gut in regular sleep is limited therefore, researchers at the University of Tsukubai in Japan analysed in mice ‘whether the gut microbiota contributes to our sleep/wake cycle’.
Male mice were randomly split into two group, a control (n = 12) and an experimental group (n = 13) group. The experimental group was treated in a four-week period with four types of broad-spectrum antibiotics, which produced antibiotic-induced microbiota-depleted (AIMD) mice. Both groups were fed the same and were in the same environment. An electrode was inserted into the brain of each mouse, which produced electroencephalogram (EEG)/electromyogram (EMG) signals. This allowed the analysis of different parts of the sleep/wake cycle (such as non-rapid eye movement sleep (NREMS) and rapid eye movement sleep (REMS)). Additionally, caecal contents (contents of the caecum – a pouch in the peritoneum at the beginning of the large intestines), of the control and the experimental group were collected and analysed, as metabolites are found here.
Analysis of the EEG/EMG signals demonstrated that the AIMD mice spent less time in NREMS (a dreamless sleep with a slow and regular heart rate and low blood pressure) during the sleeping phase of a mouse and during their awake phase, a longer period of time was spent in the NREMS in comparison to the control group. This suggests that the circadian rhythmicity (a biological process that regulates the sleep/wake cycle which is repeated roughly every 24 hours) was reduced in the AIMD mice. This led the researchers to suggest that ‘AIMD promotes the fragmentation of NREMS’ in the sleep phase. However, the total amount of time required to be spent in the awake phase and NREMS phase within a 24-hour period did not change.
The researchers found that serotonin (a neurotransmitter which plays a role in the sleep/wake regulations) was shown to have been significantly depleted. Extremely low levels of serotonin reduces the amount of time spent in the NREMS during the sleep phase of the mice and increases the amount of time spent in the awake phase, without changing the time required for each phase in a 24-hour span. This allowed the researchers to suggest that serotonin may be involved in the communication between the gut microbiota and sleep. Additionally, the researchers suggest that the serotonin depletion (caused by a reduction in dietary tryptophan (found in chicken, cheese, milk etc..) and in a low vitamin-B6 environment) causes there to be more time spent in the REMS in AIMD mice. The way in which serotonin in the brain affects the sleep/wake cycle needs further investigation. Analysis of the caecum also showed fluctuations in the levels of neurotransmitters such as GABA, dopamine and glycine which, play a role in gut physiology such as blood flow to the gut, this led the researchers to suggest that this may have an effect on the sleep/awake cycle.
This study displayed that the gut microbiota plays a role in our sleep. Dysbiosis of the gut microbiota can not only be caused by antibiotics but also by our diet and may affect our regular sleep. This finding has the potential to help those who suffer with sleep disorders such as insomnia, as changes to the gut microbiota could improve these disorders. More research is required into the role serotonin plays in the communication between the gut and sleep, which metabolites in the gut microbiota affect the circadian clock and how intestinal neurotransmitters affect our sleep/wake cycle. Next time you are experiencing some daytime sleepiness, assess the food you have ingested – it may have had an effect on your gut microbiota.
Original Source: Ogawa, Y., Miyoshi, C., Obana, N. et al. Gut microbiota depletion by chronic antibiotic treatment alters the sleep/wake architecture and sleep EEG power spectra in mice. Sci Rep 10, 19554 (2020). https://doi.org/10.1038/s41598-020-76562-9
Feature Image Source: GettyImages
Edited by Cyrus Rohani-Shukla