The gut microbiota forms part of a complex network termed the microbiota-gut-brain axis along with the enteric nervous system, sympathetic and parasympathetic divisions of the autonomic nervous system, neuroendocrine and neuroimmune components the central nervous system. The gut microbiota is associated with neuropsychiatric disorder such as schizophrenia, autistic disorders, anxiety disorders, major depression and bipolar disorder.

It is evident that the microbiota plays a key role in HPA axis activity and immune response. However, the mechanism of modulating physiological response at a central level is unresolved. Crosstalk possibly include dynamic molecules with multiple effector mechanisms that can communicate in local environment to regulate a complex coordinated response on multiple physiological systems. Potential mechanisms might include changes in microbial content, immune stimulation, neural pathways (via the vagus nerve), tryptophan metabolism, gut hormonal response, and bacterial metabolites.

Major depressive disorder is a stress-related mood disorder associated with a disrupted HPA axis, and evidence suggests that the gut microbiota play a key role in modulating depression. Bipolar disorder is a severe psychiatric disorder with dysfunctions of neuroimmune system which also suggest the brain-gut-microbiota axis is an important physiological mechanism.

In this Research Topic, we welcome the latest scientific contributions, including original research, systematic reviews, meta-analyses. We also welcome clinical and pre-clinical studies as well as basic research in humans and / or animals.

Keywords: neuro-immune, brain-gut axis, microbe, depressive disorder, bipolar disorder

Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.