THE INFLUENCE OF THE GUT MICROBIOTA ON NEUROTRANSMITTER SYNTHESIS AND NERVOUS SYSTEM PHYSIOLOGY

The gut microbiota is a complex microbial ecosystem involved in digestion, metabolism, immune homeostasis, and communication with the nervous system. Evidence from microbiological, physiological, and biochemical research indicates that intestinal microorganisms can influence neuroactive compound production, neurotransmitter metabolism, and signalling along the microbiota–gut–brain axis. Serotonin, gamma-aminobutyric acid (GABA), dopamine, noradrenaline, and glutamate are among the compounds and pathways investigated in this context. Microbial effects may involve amino-acid metabolism, short-chain fatty acid production, enteroendocrine-cell activity, immune mediators, the enteric nervous system, and vagal signalling. Importantly, neurotransmitters produced in the intestine do not necessarily enter the brain directly; peripheral and central neurotransmitter pools are regulated differently. This review summarizes key mechanisms linking the gut microbiota with neurotransmitter-related pathways and nervous system physiology, while distinguishing experimental findings from conclusions that remain uncertain in humans.