There really is something to the concept of having a gut feeling. New research out today suggests our bodies can directly sense and communicate with the many bacteria lining our digestive tract.
Scientists at Duke University led the study, published Wednesday in Nature. They found that nerve cells can respond in real time to bacterial signals from the gut—including signals that tell us to curb our appetite. The findings suggest the relationship we have with our microbial neighbors is even more complex than thought, the researchers say.
Humans are well known for having five basic senses (sight, hearing, touch, smell, and taste). But according to the study researchers, growing evidence points to other senses that react specifically to cues from our digestive system, the “gut sense.”
Some of the researchers had previously discovered that certain cells lining the gut can sense specific stimuli and directly communicate with nearby nerve cells that lead back to the brain, called neuropods. And they reasoned that one type of stimuli these cells detect would be the gut microbiome, the trillions of normally harmless, often helpful bacteria and other microbes that live inside us.
“We had previously found that neuropod cells in the small intestine sense and rapidly respond to nutrients,” co-lead author Maya Kaelberer, a sensory neuro-gastroenterologist, told Gizmodo. “It seemed natural to think that neuropod cells of the colon could sense the gut microbiome; therefore, we set out to find out how.”
The team focused on an ancient protein found in the tail, or flagella, of many gut bacteria, aptly named flagellin. Gut bacteria appear to produce more flagellin when we eat, and neuropods can detect flagellin through a receptor called the Toll-like receptor 5 (TLR5), the researchers found. In experiments with mice, they also showed that this interaction seems to be key to regulating our hunger.
When the researchers gave fasting mice flagellin directly through the colon, for instance, the mice ate less than usual. They then knocked out the TLR5 receptor in neuropods and ran the same experiment, finding that the mice now kept eating and gained weight.
The findings indicate that increased levels of bacterial flagellin act as a real-time signal for the brain to tamp down our hunger. Neuropods catch this signal through the TLR5 receptor and then quickly transmit it to the brain via the vagus nerve. If the neuropods’ ability to detect nutrients could be considered a sixth sense, then its detection of gut microbes might be a distinct, seventh sense, the researchers argue.
“We discovered that our colon has a sense for microbes, the neurobiotic sense,” Kaelberer said.
More research is needed to confirm and better understand how this neurobiotic sense operates in people, of course. But assuming it’s genuine, the discovery would have important scientific and medical implications. Certain health conditions might alter the communication between gut bacteria, neuropods, and the brain, for instance, as might things like our diets or environment. And perhaps someday, we’ll be able to safely influence this sense to treat or prevent such conditions.
“If you lived in a world where everything you saw was blue—blue walls, blue ground, blue computers, blue cars… Then you come home to see a yellow/orange peach on your blue table; it would have a profound effect on your experience. Knowing this, can we target this sense to have that same profound experience without the peach?” Kaelberer said.
This is still just the beginning of the team’s exploratory work. They next hope to uncover whether neuropods can also detect immune-related signals. In the meanwhile, I’ll be sure to thank my gut bacteria from now on for helping me have at least some restraint when it’s time for dessert.
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