Metabolomic insights into gut-brain axis dysregulation under unpredictable chronic stress in zebrafish.

Growing evidence indicates that depression is closely associated with disturbances in the gut-brain axis. Although rodent models are currently widely utilised in depression pathophysiology research, the zebrafish (Danio rerio) has become a valuable and promising alternative model species. This study examined changes in neuroendocrine and neurochemical markers associated with behavioural modifications in a zebrafish model of unpredictable chronic stress (UCS). Following a 14-day UCS procedure, the open-field test (OFT), social interaction test (SIT), and light-dark test (LDT) were conducted. Whole-body cortisol and IL-1β levels, along with metabolomics analysis of brain and intestinal tissues, were performed for neuroendocrine and neurochemical assessment. Depression-like behaviours such as increased immobility time (P = 0.0009) and impaired social interaction (P = 0.0306) were observed, alongside elevated levels of cortisol (P < 0.0001) and IL-1β (P = 0.0255). NMR-based metabolomics analysis revealed alterations in valine, alanine, glutamate, and choline in both brain and intestinal tissues in UCS zebrafish, indicating disruption of amino acid metabolism, highlighting the involvement of bidirectional gut-brain axis communication. The glycine, serine, and threonine pathways were most significantly perturbed in UCS zebrafish, suggesting compromised redox homeostasis leads to neuroinflammation in the pathophysiology of depression-related chronic stress related to the gut-brain axis. This study demonstrates that zebrafish is a valuable alternative vertebrate model for exploring the systemic impacts of unpredictable chronic stress (UCS) on the gut-brain axis.