Gut-brain connection in schizophrenia: A narrative review

Table 2 Key gut-derived metabolites, their bacterial sources, their function in the brain, and how they impact mental health and cognition[81,82]

Metabolite	Source (gut bacteria)	Role in the brain	Influence on mental health and cognition
Butyrate	Firmicutes (e.g., Clostridium, Faecalibacterium)	Modulates neuroinflammation, supports neuronal health, regulates neurotransmitter release	Enhances neuroprotection, reduces neuroinflammation, and supports cognitive function; potential to alleviate mood disorders
Gamma-aminobutyric acid	Lactobacillus, Bifidobacterium	Inhibitory neurotransmitter, regulates mood, anxiety, and central GABAergic signaling	Reduces anxiety and stress responses; GABA imbalance linked to mood disorders like depression and anxiety
Homovanillic acid	Bifidobacterium longum	Dopamine metabolite, involved in synaptic integrity and reward pathways	Alleviates depressive symptoms, enhances emotional regulation, and protects synaptic health
Serotonin	Enterococcus, Escherichia, Streptococcus	Regulates mood, cognition, and motor control	Deficiency linked to depression and anxiety; essential for mood regulation and emotional well-being
Acetylcholine	Gut bacteria involved in producing precursors (Lactobacillus, Bifidobacterium)	Key neurotransmitter for motor control, learning, and memory	Deficiency associated with cognitive decline, memory disorders, and Alzheimer’s disease

GABA: Gamma-aminobutyric acid.