Relief from Chronic Unpredictable Mild Stress-Induced Constipation by Fluoxetine and Butyrate and Their Impact on Gut Microecology.

PURPOSE: This study investigated fluoxetine (FLX) effects on chronic unpredictable mild stress (CUMS)-induced depression and constipation, and to explore the potential synergistic benefits of combining FLX with butyrate supplementation. METHODS: A mouse model of CUMS and functional constipation (FC) was established. Behavioral assessments, fecal parameters, colonic transit time, and histological analysis were performed. Serotonin signaling, gastrointestinal hormones, intestinal barrier function, and inflammatory markers were measured. Gut microbiota composition was assessed using 16S rRNA sequencing, and fecal short-chain fatty acid (SCFA) levels were quantified by gas chromatography-mass spectrometry. RESULTS: FLX significantly alleviated depressive-like behaviors (40% reduction in immobility time) and improved gastrointestinal motility (35% increase in fecal pellet output) in CUMS-FC mice. FLX restored serotonin signaling (2.5-fold increase in 5-HT levels), enhanced intestinal barrier integrity (60% upregulation of ZO-1/Occludin), and increased gut microbial diversity (Shannon index increased by 30%). FLX elevated butyrate-producing bacteria and fecal butyrate levels by 45%. Notably, the novel FLX-butyrate combination produced synergistic effects, achieving 65% improvement in gut motility, 70% reduction in pro-inflammatory cytokines (IL-1β, TNF-α, IL-6), and 80% restoration of intestinal barrier function compared to FLX alone. CONCLUSION: FLX alleviates CUMS-induced depression and constipation through restoring serotonin signaling, modulating gut microbiota toward SCFA production, and improving intestinal barrier function. The novel synergistic enhancement achieved by FLX-butyrate combination demonstrates superior therapeutic efficacy, highlighting its potential as an innovative dual-targeting strategy for gut-brain axis disorders.