Belly bacteria boss the brain

Friendly intestinal bacteria not only keep the gut happy, they may help keep their host happy, too, a new study in mice finds.

Mice fed broth fortified with a type of friendly intestinal bacteria called Lactobacillus rhamnosus behaved less anxiously than mice fed broth without bacteria. Those behavior changes were accompanied by differences in levels of a brain-chemical sensor and stress hormones.

The bacteria telegraph these brain-chemical and behavior-changing messages via the vagus nerve, which connects the brain stem to various internal organs, researchers report online August 29 in the Proceedings of the National Academy of Sciences.

Some studies have suggested that changing the mix of bacteria in the intestines could influence behavior (SN: 6/18/11, p. 26). The new research goes a step further to investigate how those changes come about, says Paul Patterson,