Gut Microbiome and Psychiatric Disorders

In the past decade, considerable advances have been made in understanding how the gut–brain–immune axis and its resident microbiome influence behavior. This chapter first provides an overview of the basic development and organization of the gut–brain–immune system in humans. The interactions of host cells and commensal bacteria are emphasized, spanning classical neurotransmitters and metabolites as well as novel molecular mechanisms. Then, current methods of studying the microbiome are reviewed, and representative data illustrating differences between two common methods (16S and shotgun sequencing) are provided across different ages. The data indicate that the core oral microbiome undergoes considerable modification from childhood to adulthood. Additional contrasts between oral and fecal microbiome data are provided, which highlight the utility of functional microbiome profiling. Finally, recent findings from studies of microbiome changes in several major neuropsychiatric conditions are summarized and compared, and some recommendations are offered to help guide future research and clinical applications.