A ketamine/methionine exposure paradigm, alone or combined with Lactobacillus rhamnosus GG, assessing schizophrenia-relevant behavioral, oxidative stress, and molecular endpoints in adult zebrafish.

BACKGROUND

Schizophrenia (SCZ) is a multifactorial neuropsychiatric disorder involving glutamatergic dysfunction, oxidative imbalance, impaired cellular plasticity, and neuron-glia interactions. Adult zebrafish provide a translational vertebrate model for investigating SCZ-relevant behavioral and biological domains. This study evaluated the effects of repeated ketamine (KET) and methionine (MET) exposure, administered alone or combined with Lactobacillus rhamnosus GG (LGG), on behavioral, oxidative, transcriptional, histopathological, and immunofluorescence (IF) endpoints.

METHODS

Adult zebrafish were repeatedly exposed to KET (20/40 mg/L) or MET (4.5/6.0 mM), with or without LGG (5 × 109 CFU). Behavioral responses were assessed using the mirror-induced aggression (MIA) and novel tank test (NTT). Oxidative stress biomarkers (superoxide dismutase - SOD, glutathione peroxidase - GPx, and malondialdehyde - MDA), gene expression (PCNA, CAT, TP53, and SOD1), Luxol Fast Blue-Cresyl Violet (LFB-CV) histopathology, and IF analyses (BLBP and SOX2) were performed.

RESULTS

Repeated KET exposure predominantly altered mirror-directed social responsiveness and vertical exploration, whereas MET produced comparatively modest behavioral effects despite inducing more pronounced oxidative and proliferative alterations. Oxidative responses included reduced SOD activity, selective GPx activation, and increased lipid peroxidation. PCNA was the most responsive transcriptional marker, while CAT, SOD1, and TP53 showed limited changes. Histopathological analyses revealed alterations in myelin-associated staining, neuronal integrity, tissue architecture, and neuronal loss. LGG partially attenuated selected oxidative and structural alterations but produced limited behavioral effects.

CONCLUSIONS

Repeated KET and MET exposure generated distinct yet complementary SCZ-relevant behavioral and biological profiles in adult zebrafish, supporting their utility for investigating glutamatergic dysfunction, metabolic stress, and gut-brain interactions.