Alcohol-fluoxetine co-treatment drives gut dysbiosis and intestinal barrier disruption with consequences for neuroimmune signaling in male rats.

Alcohol consumption and depression frequently co-occur, but little is known about how alcohol and antidepressant medication interact along the gut-brain axis. We examined the independent and combined effects of chronic alcohol exposure and fluoxetine on gut microbiota, intestinal structure, peripheral endotoxin-related and inflammatory markers, and neuroinflammatory gene expression in male rats. Animals received alcohol for 14 days and fluoxetine for 7 days, resulting in four groups: control-vehicle, control-fluoxetine, alcohol-vehicle, and alcohol-fluoxetine. Fecal microbiota was analyzed using 16S rRNA sequencing, functional prediction, and culturable bacteria under antibiotic selection. Ileal morphology, extracellular matrix organization, plasma LPS and cytokines, and neuroinflammation-related gene expression in the amygdala and medial prefrontal cortex (mPFC) were also evaluated. Both alcohol and fluoxetine modified the gut microbiota, with their combination producing the most pronounced alterations, including the loss of several short-chain fatty acid-producing taxa. Fluoxetine alone increased alpha diversity and altered the abundance of genera linked to metabolic activity. Alcohol impaired intestinal integrity by reducing villus width, increasing goblet cell density, and decreasing collagen content. In animals with prior alcohol exposure, reduced plasma LPS and TNF-α levels were observed at the time of sample collection. Neuroimmune gene expression changes differed between the amygdala and mPFC, indicating region-specific central responses. Together, these findings reveal that fluoxetine treatment can modulate the gut-brain axis differently depending on prior alcohol exposure, supporting further investigation of microbiota-related mechanisms in alcohol use and psychiatric comorbidity.