The Microbiota/Microbiome and the Gut–Brain Axis: How Much Do They Matter in Psychiatry?

Abstract

The functioning of the central nervous system (CNS) is the result of the constant integration of bidirectional messages between the brain and peripheral organs, together with their connections with the environment. Despite the anatomical separation, gut microbiota, i.e., the microorganisms colonising the gastrointestinal tract, is highly related to the CNS through the so-called “gut–brain axis”. The aim of this paper was to review and comment on the current literature on the role of the intestinal microbiota and the gut–brain axis in some common neuropsychiatric conditions. The recent literature indicates that the gut microbiota may affect brain functions through endocrine and metabolic pathways, antibody production and the enteric network while supporting its possible role in the onset and maintenance of several neuropsychiatric disorders, neurodevelopment and neurodegenerative disorders. Alterations in the gut microbiota composition were observed in mood disorders and autism spectrum disorders and, apparently to a lesser extent, even in obsessive-compulsive disorder (OCD) and related conditions, as well as in schizophrenia. Therefore, gut microbiota might represent an interesting field of research for a better understanding of the pathophysiology of common neuropsychiatric disorders and possibly as a target for the development of innovative treatments that some authors have already labelled “psychobiotics”.

Gut Microbiome: A Brief Review on Its Role in Schizophrenia and First Episode of Psychosis

“…Considering that (a) the gut is the most dynamic immunological environment in the body, (b) gut microbiome colonisation early in life is critical for the optimal development of the immune system [39], and (c) that dysbiosis of the intestinal ecosystem may affect immune responses [40], dysfunctions such as chronic inflammation and oxidative stress, which have been implicated in schizophrenia, are proposed to be, at least in part, associated with changes in the microbiome [14]. These include the microbiome's mediation in the regulation of pro-inflammatory cytokines, which may, in turn, influence the pathophysiology of mental disorders [16]; for example, increased IL-6, IL-1β and IL-2R concentrations are reported in chronic schizophrenic patients [41].…”

Effect of stigma maydis polysaccharide on the gut microbiota and transcriptome of VPA induced autism model rats

“…In addition, the functional enrichment analysis of 16S rRNA profile suggested that SMPS intervention affected biological metabolism (including starch and sucrose metabolism, biosynthesis of amino acids, galactose metabolism and other glycan degradation pathways) through regulating intestinal flora. Interestingly, the recent literature indicated that the gut microbiota had effect on brain functions through endocrine and metabolic pathways and the enteric network, especially in the onset and maintenance of neurodevelopment and neurodegenerative disorders (Marazziti et al, 2021). ASD is a neurodevelopmental disease.…”

Acute Cold Water-Immersion Restraint Stress Induces Intestinal Injury and Reduces the Diversity of Gut Microbiota in Mice

“…The GM is a diverse and dynamic microbes’ population with extensive and essential interactions with the digestive, immune, and nervous systems ( Huo et al., 2017 ; Marazziti et al., 2021 ). The complex bidirectional communication systems between the GI tract and the brain were initially termed “gut-brain axis” and then renamed “microbiota-gut-brain axis”, considering the pivotal role of GM in sustaining local and systemic homeostasis ( Lavelle and Sokol, 2020 ; Banfi et al., 2021 ).…”