Effects of intestinal microbiota on anxiety-like behavior.

The acquisition of intestinal microbiota in the immediate postnatal period has a defining impact on the development and function of many immune and metabolic systems integral to health and well-being. Recent research has shown that the presence of gut microbiota regulates the set point for hypothalamic-pituitary-adrenal (HPA) axis activity.1 Accordingly, we sought to investigate if there were other changes of brain function such as behavioral alterations in germ free (GF) mice, and if so, to compare these to behavior of mice with normal gut microbiota. Our recent paper showed reduced anxietylike behavior in the elevated plus maze (EPM) in adult GF mice when compared to conventionally reared specific pathogen-free (SPF) mice.2 Here, we present data collected when we next colonized the adult GF mice with SPF feces thereby introducing normal gut microbiota, and then reassessed anxiety-like behavior. Interestingly, the anxiolytic behavioral phenotype observed in GF mice persisted after colonization with SPF intestinal microbiota. These data show that gut-brain interactions are important to CNS development of stress systems and that a critical window may exist after which reconstitution of microbiota and the immune system does not normalize the behavioral phenotype.