Environmental levels of the antibiotic enrofloxacin triggered anxiety-like behavior in zebrafish by disrupting the gut microbiome and altering key peptide hormones including GLP-1, neuropeptide Y, and stress hormones.
Multiple peptide pathways disruptedAntibiotic exposure altered GLP-1 and 5-HT in the gut, ACTH and cortisol in blood, and CRH, BDNF, and NPY in the brain — all from a single environmental exposure
What the researchers found
Zebrafish exposed to the antibiotic enrofloxacin at environmentally realistic levels (60 μg/L for 28 days) developed anxiety-like behaviors in two standard behavioral tests. The antibiotic disrupted the gut microbiome by increasing Bacteroidetes and lowering the Firmicutes/Bacteroidetes ratio, while significantly altering multiple peptide signaling molecules: intestinal GLP-1, 5-HT, IL-6, and TNF-α were elevated, plasma ACTH and cortisol were reduced, and brain levels of CRH, BDNF, and neuropeptide Y were increased — suggesting the microbiota-gut-brain axis mediated the behavioral changes.
Why it matters
This study shows how environmental antibiotic contamination can disrupt gut bacteria in ways that alter peptide hormone signaling throughout the body and brain, ultimately changing behavior. It highlights the interconnectedness of the microbiome, gut peptides like GLP-1, and brain neuropeptides like NPY in regulating mood and anxiety.
The numbers in context
60 μg/L enrofloxacin · 28-day exposure · Elevated GLP-1, 5-HT, IL-6, TNF-α in gut · Reduced ACTH and cortisol in plasma · Elevated CRH, BDNF, NPY in brain
How the study worked
Zebrafish were exposed to enrofloxacin at 6 and 60 μg/L for 28 days. Anxiety-like behavior was measured using light-dark test and novel tank task. Gut microbiome composition was analyzed. Intestinal, plasma, and brain levels of multiple peptides and signaling molecules were measured.
Who was studied
Zebrafish exposed to environmentally realistic concentrations of enrofloxacin
What this study cannot tell us
Zebrafish study — results may not directly translate to humans. The antibiotic used (enrofloxacin) is primarily veterinary. Correlation between microbiome changes and peptide alterations does not prove causation. Sample size not specified in abstract. No germ-free controls to confirm microbiome-mediated mechanism.
How to read the evidence
This is an early-stage animal study using zebrafish, which are a common model organism but far removed from human physiology. The correlational design cannot confirm that microbiome changes caused the peptide alterations or the behavioral changes.
When this study was published
Published in 2023, this is a recent study that reflects current interest in the microbiota-gut-brain axis and environmental toxicology. The peptide signaling pathways it examines remain active areas of research.
The bigger picture
This research adds to the growing evidence that gut bacteria communicate with the brain through peptide hormones. It demonstrates that environmental disruptions to the microbiome — even from low-level antibiotic exposure — can ripple through the entire peptide signaling network, affecting GLP-1 in the gut, stress peptides in the blood, and neuropeptides in the brain. This has implications for understanding how environmental toxins might contribute to anxiety and mood disorders.
Questions still open
- Do antibiotic residues in drinking water affect gut peptide signaling and mood in humans at similar environmental concentrations?
- Could probiotic restoration of the Firmicutes/Bacteroidetes ratio reverse the peptide signaling disruptions and anxiety behaviors?
- Which specific peptide pathway changes — GLP-1, NPY, or CRH — are most directly responsible for the observed anxiety-like behaviors?
Common questions
How does an antibiotic in water affect brain peptides like neuropeptide Y?
Should I be worried about antibiotics in my drinking water?
Read the original research
Enrofloxacin exposure induces anxiety-like behavioral responses in zebrafish by affecting the microbiota-gut-brain axis.
The Science of the total environment, 858(Pt 3), 160094
Citation
Tian, Dandan; Shi, Wei; Yu, Yihan; Zhou, Weishang; Tang, Yu; Zhang, Weixia; Huang, Lin; Han, Yu; Liu, Guangxu. (2023). Enrofloxacin exposure induces anxiety-like behavioral responses in zebrafish by affecting the microbiota-gut-brain axis.. The Science of the total environment, 858(Pt 3), 160094. https://doi.org/10.1016/j.scitotenv.2022.160094