Gut microbiota include all microorganisms inhabiting the intestinal tract as well as their genomes. Although bacteria predominate the microbiome, viruses, phages and fungi are likewise included among the trillions of microorganisms that populate our intestine. In the past 10 years, accumulating interest in the function of the gut flora has revealed numerous physiologic functions including nutrition, digestion, inflammation, growth, immunity and protection against infections and illness.
Conversely, deficits in communication between microbiota and other systems could play a role in acquiring disorders such as metabolic derangement (obesity diabetes mellitus), autoimmune disorders and neuropsychiatric disorders such as anxiety, major depressive disorders and autism spectrum disorders. The complex and bidirectional networks between gut microorganisms and their host have shed some light on the mechanisms by which environment influences the central nervous system’s physiology and psychopathology.
It is not known how the microbiota and the central nervous system communicate. Theories include via autonomic, neuroendocrine, enteric and immune systems, with pathology resulting in disruption to neurotransmitter balance. The increase in chronic inflammation or exacerbated hypothalamic-pituitary-adrenal axis activity is an entirely new area of investigation, but it has promising potential. Well controlled rodent studies do not reflect the multifaceted complexity germane to human pathophysiology, particularly neuropsychiatric dysfunction and health.
Why Does This Matter?
The emphasis on neurological and behavioral impairment rooted in our limited understanding of the role and functional mechanisms of the gut-brain axis will require much more basic science.
At present, the limited experimental and clinical data attained from therapeutic manipulation of the microbiome to treat specific mental health disorders are described, as are important gaps in knowledge and next steps.