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Misera et al. Microbiome Res Rep 2024;3:48 https://dx.doi.org/10.20517/mrr.2023.81 Page 5 of 19

Figure 1. Stress vulnerability model. Created with BioRender software.

[39]
formation of each individual’s gut microbiota . Despite this, scientists are discovering more and more
common traits and are gaining a better understanding of the individual microbiota and its impact on bodily
function and health, both physical and mental .
[40]
The microbiota significantly impacts the formation and modulation of the gut-brain axis . Researchers
[41]
have found that the gut microbiota is also involved in developing the hippocampus responsible for memory,
the amygdala as the brain’s alarm center, and the myelination processes of prefrontal cortex neurons
responsible for executive functions [42,43] . Furthermore, the metabolic activity of the microbiota is comparable
to that of the liver. The microorganisms that make up the intestinal ecosystem break down undigested food
residues by fermentation and actively and rapidly eliminate harmful antigens in the intestinal lumen. The
intestinal microbiota produces vitamin K and B vitamins and, by producing hydrolase, aids in the efficient
digestion of lipids. Pivotal metabolites are SCFAs, which are essential for adequately functioning of
intestinal cells. Microbes stimulate the synthesis of mucins, which protect the endothelium from invasion by
pathogens and toxins. In addition, they affect the CNS by producing and modulating the concentration of
selected neuromediators such as serotonin, histamine, acetylcholine, norepinephrine, melatonin, and
gamma-aminobutyric acid (GABA). They also affect the expression of receptors for these neurotransmitters
[44]
in the brain by stimulating immune cells to release pro- and anti-inflammatory cytokines . Furthermore,
the gut microbiota impacts blood cortisol levels, affecting the functioning of various organs and