The Role of Gut Microbiota in Regulating Nervous System Function: A Review of Molecular Mechanisms and Key Bacterial Species

Gut microbiota is a complex community of microorganisms that plays a pivotal role in maintaining systemic homeostasis. The bidirectional communication between the gut and the brain, known as gut–brain axis, involves neural, immune, hormonal, and metabolic pathways. In recent years, alterations in microbial composition (dysbiosis) have been increasingly associated with psychiatric disorders such as anxiety, depression, and stress-related conditions. Among the key mediators of this interaction are short-chain fatty acids (SCFAs), which exert neuroprotective effects by strengthening the blood–brain barrier, modulating inflammatory pathways (NF-κB, Nrf2), and inducing epigenetic changes in genes related to neuroplasticity. Furthermore, the microbiota influences mood and stress responses through immune regulation and modulation of neurotransmitters such as GABA and serotonin. This review highlights the roles of key bacterial species, including Lactobacillus rhamnosus, Bifidobacterium longum, and Faecalibacterium prausnitzii, as principal regulators of the gut–brain axis. Clinical evidence indicates that simple dietary interventions and probiotic supplementation can alleviate psychological symptoms and reduce stress. This review emphasizes the molecular mechanisms and clinical findings that link gut microbiota to the pathogenesis and treatment of stress-related disorders, and it provides perspectives on the potential use of probiotics, prebiotics, and nutritional strategies.