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The recent findings regarding peptidoglycan, or PG, lend weight to that hypothesis and point to a possible regulatory role for bacterial cell wall products in sleep. Credit: Neuroscience News<\/p>\nSummary: A new study shows that bacterial cell wall molecules, specifically peptidoglycan, are present in the brain and fluctuate with sleep cycles. This finding supports a hypothesis that sleep is not solely brain-regulated but arises from the interplay between the body and its microbiome.<\/p>\n
Researchers propose this \u201cholobiont condition\u201d model, where microbial and neurological systems together govern when and how we sleep. The work not only reframes sleep science but also connects microbes to cognition, behavior, and even the evolution of sleep itself.<\/p>\n
Key Facts<\/p>\n
Peptidoglycan Link: Bacterial cell wall molecules were found in mouse brains, aligning with sleep cycles.Holobiont Hypothesis: Sleep may result from brain\u2013microbe interactions, not just brain activity alone.New Paradigm: Findings suggest microbes shaped the evolution of sleep and influence cognition and behavior today.<\/p>\n
Source: Washington State University<\/p>\n
What causes us to sleep? The answer may lie not only in our brains, but in their complex interplay with the micro-organisms spawned in our intestines.<\/p>\n
New research from Washington State University suggests a new paradigm in understanding sleep, demonstrating that a substance in the mesh-like walls of bacteria, known as peptidoglycan, is naturally present in the brains of mice and closely aligned with the sleep cycle.<\/p>\n
The recent findings regarding peptidoglycan, or PG, lend weight to that hypothesis and point to a possible regulatory role for bacterial cell wall products in sleep. Credit: Neuroscience News<\/p>\n
Those findings serve to update a broader hypothesis that has been in development at WSU for years\u2014proposing that sleep arises from communication between the body\u2019s sleep regulatory systems and the multitude of microbes living inside us.<\/p>\n
\u201cThis added a new dimension to what we already know,\u201d said Erika English, a PhD candidate at WSU and lead author on two recently published scientific papers introducing the findings.<\/p>\n
This view of sleep as arising from that \u201cholobiont condition\u201d joins a growing body of evidence suggesting that our gut microbiomes play an important role in cognition, appetite, sex drive and other activity\u2014a view that turns traditional brain-centric models of cognition upside-down and has implications for our understanding of evolution and free will, as well as the development of future treatments for sleep disorders.<\/p>\n
The recent findings regarding peptidoglycan, or PG, lend weight to that hypothesis and point to a possible regulatory role for bacterial cell wall products in sleep. PG is known to promote sleep when injected in animals, but until recently, the conventional view held that it did not naturally migrate to the brain.<\/p>\n
English found that PG, along with its receptor molecules involved in PG signaling and communication, was present in different locations within the brain, at levels that changed with the time of day and sleep deprivation.<\/p>\n
The findings were\u00a0reported in July in\u00a0Frontiers in Neuroscience;\u00a0longtime WSU sleep researcher and Regents Professor James Krueger co-authored the paper.<\/p>\n
English is also lead author of a recent paper with Krueger\u00a0in the journal\u00a0Sleep Medicine Reviews\u00a0that proposes the \u201cholobiont condition\u201d hypothesis of sleep.<\/p>\n
That paper combines two prevailing views. One posits that sleep is regulated by the brain and neurological systems. Another focuses on \u201clocal sleep,\u201d which frames slumber as the result of an accumulation of sleep-like states among small cellular networks throughout the body. Such sleep-like states have been observed among cells in vitro, known as the \u201csleep in a dish\u201d model.<\/p>\n
As these smaller pockets of sleep accumulate, like lights going off in a house, the body tips from wakefulness toward sleep.<\/p>\n
The new hypothesis merges those theories, proposing that sleep results from the interplay between the body and its resident micro-organisms\u2014two autonomous systems that interact and overlap.<\/p>\n
\u201cIt\u2019s not one or the other, it\u2019s both. They have to work together,\u201d English said. \u201cSleep 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.\u201d<\/p>\n
Links between the microbiome and behavior are emerging on several fronts, indicating that micro-organisms formed in the gut play an important role in cognition and fundamental human behaviors.<\/p>\n
This work upends the traditional view of human neurology, suggesting that it is not completely top-down\u2014i.e., the result of decision-making in the brain\u2014but bottom-up\u2014i.e., driven by the tiny organisms whose evolution shaped animals to serve as their hosts and whose needs influence the activities and cognition of their hosts.<\/p>\n
\u201cWe have a whole community of microbes living within us. Those microbes have a much longer evolutionary history than any mammal, bird or insect \u2013 much longer, billions of years longer,\u201d said Krueger, who was named a \u201cLiving Legend in Sleep Research\u201d by the Sleep Research Society in 2023.<\/p>\n
\u201cWe think sleep evolution began \u00a0eons ago with the activity\/inactivity cycle of bacteria, and the molecules that were driving that are related to the ones driving cognition today.\u201d<\/p>\n
English\u2019s work expands upon known links between bacteria and sleep, including the fact that sleep patterns affect the function of the gut microbiome and that bacterial infections cause people to sleep more.<\/p>\n
The new findings begin to delve into questions that English looks forward to exploring further.<\/p>\n
\u201cNow that the world has come to appreciate how important microbes are, not just for disease but also for health, it\u2019s a very exciting time to start to expand on our understanding of how we are communicating with our microbes and how our microbes are communicating with us,\u201d she said.<\/p>\n
About this sleep and neuroscience research news<\/p>\n
Author: Shawn Vestal<\/a>
Source: Washington State University<\/a>
Contact: Shawn Vestal \u2013 Washington State University
Image: The image is credited to Neuroscience News<\/p>\n