Gut-brain axis in psychiatric disorders

Emerging evidence links gut microbiome composition to psychiatric symptoms through multiple pathways: vagus nerve signaling, short-chain fatty acid production, tryptophan metabolism affecting serotonin synthesis, and immune system modulation. However, establishing causal direction remains difficult, and clinical trials of probiotics and fecal microbiota transplantation for depression show inconsistent results. Standardizing microbiome measurement, identifying mechanistically relevant bacterial strains, and designing adequately powered interventional studies are key bottlenecks.