Specific Gut Bacteria Influence Oxytocin Levels
Circulating oxytocin levels decline with age, and a number of research groups have demonstrated that oxytocin upregulation produces benefits in animal studies. Here, researchers provide evidence for a species of bacteria resident in the intestine to contribute to changes in oxytocin expression and secretion. As the balance of different microbial populations of the gut change with age, this might lead to ways to restore more youthful levels of oxytocin in the body via manipulation of the gut microbiome.
The gut microbiome, a community of trillions of microbes living in the human intestines, has an increasing reputation for affecting not only gut health but also the health of organs distant from the gut. For most microbes in the intestine, the details of how they can affect other organs remain unclear, but for gut resident bacteria L. reuteri the pieces of the puzzle are beginning to fall into place. Researchers have found that these bacteria reduce gut inflammation in adult humans and rodent models, suppress bone loss in animal models of osteoporosis and in a human clinical trial, promote skin wound healing in mice and humans and improve social behavior in six mouse models of autism spectrum disorder.
Of those effects of L. reuteri, the abilities to promote social behavior and wound healing have been shown to require signaling by the hormone oxytocin, but little was known about how this occurs. "Oxytocin is mostly produced in the hypothalamus, a brain region involved in regulating feeding and social behavior, as well as in other organs. Given that other brain-produced hormones also are made in the gut, we tested the novel idea that oxytocin itself was also produced in the intestinal epithelium where L. reuteri typically resides."
The researchers built up their case step by step. First, they reviewed single-cell RNA-Seq datasets of the intestinal epithelium, which show which genes are expressed in that tissue. They found that oxytocin genes are expressed in the epithelium of various species, including mice, macaques, and humans. Then, using fluorescence microscopy, the team revealed the presence of oxytocin directly on human intestinal organoids, also called mini guts, which are laboratory models of intestinal tissue that recapitulate many of its functions and structure. "We also determined a mechanism by which L. reuteri mediates oxytocin secretion from human intestinal tissue and human intestinal organoids. L. reuteri stimulates enteroendocrine cells in the intestine to release the gut hormone secretin, which in turn stimulates another intestinal cell type, the enterocyte, to release oxytocin."