September 30, 2011

Bacteria and Behavior

Recent research in the realm of gut bacteria has revealed amazing connections between your gut and your behavior.  Practitioners in functional medicine have long known about the gut-brain axis, as has really anyone dealing with irritable bowel syndrome. We have approximately 3 pounds of bacteria in our GI system which function synergistically to help us regulate digestion, absorption, and protection (from infection).  Bacteria also have a role in vitamin synthesis and regulation, like vitamin B6 (which is also an essential component in our body’s synthesis of neurotransmitters, like serotonin).    It appears that the bacteria in your GI system (your microbiome) might also have influence over your  biochemistry and brain development.

In one study, mice were raised in the absence of normal gut flora. Their behavior was noted to be overall less anxious than their normal gut-flora controls.  The influence appears to occur during a critical developmental window as re-colonized germ-free adults  did not reverse the behavior changes, but those re-colonized early in life manifest more anxiety typical of the normally colonized rodents.  Another study looked at the role of Lactobacillus rhamnosus , a major ingredient in many probiotic supplements. By feeding mice a broth rich in this bacteria, the mice showed fewer signs of stress and anxiety.

The exact mechanism of change is not known, but is likely mediated through the Vagus nerve.  The brains of the mice treated with L. rhamnosus showed changes in the activity of genes that encode portions of the receptor for the neurotransmitter GABA, which has an anxiolytic role.  In the germ-free mice, changes in gene expression were noted, as were corresponding changes in the neurotransmitters dopamine, serotonin, and noradrenaline in the striatum (area of the brain associated with planning and coordination of movement and actived by novel stimuli).  In all, about 40 genes were affected by the gut bacteria.

The role that these bacteria have in treating mental illness is yet to be determined, but does make one strongly consider the use of probiotic supplements for general gut (and mental) health, especially if there has been any type of antibiotic use, since antibiotics essentially denude the intestinal tract and make it ripe for recolonization by bad bacteria, yeast and fungi.

For more information on the research, please see: