The contribution of the gut-brain-microbiota axis to brain health throughout the lifespan

The gut-brain-microbiota axis (GBA) has recently been discussed as a role player in various disease states, including intestinal (such as inflammatory bowel disorder, cancer, and ulcerative colitis), extra-intestinal (such as obesity, metabolic syndrome, diabetes, and allergy), as well as several neurodegenerative, neurological, and neuropsychiatric conditions. It depicts the neural communication network between the higher brain centers and the gastrointestinal (GI) system. Perturbations in the composition of the gut microbiota mediate subsequent changes in the expression and turnover of cytokines involved in brain cognitive and immune functions. It also affects the body's reactivity to stress and other metabolic changes and disrupts the integrity of the intestinal barrier. On the other hand, the central nervous system mediates the integrity, immune homeostasis, and various functions of the gastrointestinal tract via autonomic enteric neurons. In this chapter, we highlight the interaction between the brain and the GI system through different pathways proposed for GBA, the progression of GBA across the lifespan, and shed light on the immune-mediated role of GBA in the pathogenesis of various disease outcomes with a particular focus on autism spectrum disorder, an example of neurodevelopmental disorders, schizophrenia, and depression, as examples of neuropsychiatric disorders. Sex-specific differences in disease risk and pathogenesis are discussed in detail. Additionally, as a future version, how the machine learning tools contribute to predicting the disease from microbe abundance through microbial metabolite changes.