Gut dysbiosis induced by lipopolysaccharide in zebrafish: insights into the gut-brain axis

Zebrafish (Danio rerio) are increasingly used as a vertebrate model for microbiota-gut-brain axis research due to their genetic tractability and physiological similarity to mammals. Although intrarectal delivery of chemical agents is a common approach to induce intestinal inflammation, the use of microbial components such as lipopolysaccharide (LPS) through this route in zebrafish has been relatively unexplored. In this study, we established a low-dose intrarectal LPS model (1 µg/mL) in adult zebrafish. Fish were randomly assigned to control(phosphate-buffered saline) or treatment (LPS) groups, and injections were performed under mild anesthesia. Microbiota profiling by 16S rDNA sequencing (Illumina MiSeq) identified Fusobacteriota and Firmicutes as the dominant phyla. Following LPS exposure, the Fusobacteriota increased, whereas the Firmicutes decreased, reflecting compositional shifts in the microbiota, although alpha diversity remained largely unaffected. Gene expression profiling revealed downregulation of NF-κB and upregulation of MyD88, indicating modulation of innate immune pathways. Moreover, dysbiosis was linked to changes in the expression of serotonin-related genes: tph1a, tph2, and htr1aa were significantly downregulated in the brain, with a pronounced decrease in tph2, slc6a4, and htr1aa detected in the gut. Behavioral assessment using the novel tank test demonstrated anxiogenic responses following LPS treatment. Together, these findings establish a tractable low-dose intrarectal LPS zebrafish model that induces gut dysbiosis, transcriptional changes, and behavioral alterations, providing a platform for investigating microbiota-gut-brain interactions.