hundreds of species of bacteria call the human gut their home. this gut microbiome influences our physiology and health in ways that scientists are only beginning to understand. now, a new study suggests that gut bacteria can even mess with the mind, altering brain chemistry and changing mood and behavior.

in the brains of the treated mice, the researchers found changes in the activity of genes that encode portions of the receptor for the neurotransmiter GABA. GABA typically dampens neural activity, and many drugs for treating anxiety disorders target its receptors. the pattern of changes in the GABA receptors was complicated—more GABA receptors containing a certain component in some brain regions, for example, and fewer receptors with that component in other regions—but Cryan says they’re consistent with an overall effect of reducing anxiety. none of these effects occurred in mice that ate a broth with no added bacteria.

…the changes in GABA receptors and the antianxiety effects of L. rhamnosus disappeared when the researchers cut the vagus nerve before feeding the bacteria to mice. this nerve is a major conduit of sensory information from the gut to the brain, and this experiment shows it must be intact for L. rhamnosus to have an effect on the brain. 

*via science