A study from Emory University published in March reports that live bacteria from the gut can enter the brain via the vagus nerve, according to findings released on Mar. 12. The research, conducted using mouse models, may have implications for understanding neurological health and diseases.
The study explored how an imbalanced gut microbiome, particularly one influenced by a high-fat diet similar to a Western diet, allows live bacteria to travel directly from the intestine to the brain. The vagus nerve, which connects the brainstem with major organs such as the heart and intestines, was identified as the pathway for this bacterial movement.
Ian Weiss, a microbiologist and professor at Emory University's School of Medicine, said: "This may shift the focus of new interventions for brain conditions, with the gut as the new target of the therapy. That potential anatomical shift of the target could have an unbelievable impact on how people with neurological conditions benefit from therapies."
In their experiments, researchers fed germ-free mice a diet containing 45% carbohydrates and 35% fat for nine days. This led to increased intestinal permeability—often called "leaky gut"—which enabled bacteria to move from the intestine into the brain without being detected in blood or other organs. To confirm these findings, scientists introduced a genetically marked strain of Enterobacter cloacae after administering antibiotics; this strain was later found in both the vagus nerve and brains of mice fed a high-fat diet.
The study also found low levels of bacteria in mouse models of neurological diseases such as Parkinson's Disease and Alzheimer's Disease. Researchers emphasized that strict procedures were used to prevent contamination and that bacterial counts remained low enough not to cause sepsis or meningitis.
Arash Grakoui, Ph.D., co-principal investigator and professor at Emory University, said: "This research highlights the need for further study into how dietary shifts have a huge influence on human behavior and neurological health." Grakoui added that returning mice to a normal diet reduced bacterial presence in their brains by decreasing gut permeability—a finding suggesting that some effects of high-fat diets may be reversible.
