Two Studies Report Microbes Influence the Sleep Process in Mice

Recent research from Washington State University reveals that sleep may be shaped by the interaction between the brain and micro-organisms found in the gut, rather than being solely regulated by neurological systems. Two studies highlight the discovery that peptidoglycan—a component of bacterial cell walls—is naturally present in the brains of mice and aligns closely with their sleep-wake cycles.

Traditionally, peptidoglycan was only known to promote sleep when injected into animals, and it was not believed to migrate naturally to the brain. The study demonstrated that both peptidoglycan and its receptor molecules are found in specific brain areas, with their quantities varying according to the time of day and levels of sleep deprivation.

These findings further develop a hypothesis that proposes sleep arises from communication between the body’s own sleep-regulating systems and the many microbes within the gut. Erika English, lead author on the study published in Frontiers in Neuroscience, explains that this view re-frames sleep as a phenomenon of the "holobiont condition": a state in which the host and its microbial community must coordinate for normal behavior to emerge. This conception expands on known links between the microbiome and behavior, supporting evidence that gut micro-organisms influence cognition, appetite, and other activities.

A second, related paper, published in Sleep Medicine Reviews also with English as first author, combines two leading scientific ideas: the brain-centric perspective, which posits that sleep regulation originates in neurological systems, and the concept of "local sleep," in which many pockets of sleep-like activity develop among local cellular networks throughout the body. As these sleep-like states accumulate, large-scale sleep emerges. The hypothesis advanced by English and her co-author James Krueger argues that sleep results from the overlap between the body and its resident micro-organisms—two systems that interact and overlap.

According to English, “It’s not one or the other, it’s both. They have to work together. Sleep really is a process. It happens at many different speeds for different levels of cellular and tissue organization and it comes about because of extensive coordination.” 

“We have a whole community of microbes living within us. Those microbes have a much longer evolutionary history than any mammal, bird or insect—much longer, billions of years longer,” adds Krueger. “We think sleep evolution began  eons ago with the activity/inactivity cycle of bacteria, and the molecules that were driving that are related to the ones driving cognition today.”