PPARα Antagonism Rescues Chlorpyrifos-Induced Neuro-Visual Toxicity in Zebrafish (Danio rerio) Larvae

With the global population predicted to reach 10 billion by 2050, pesticides are essential for agricultural production. However, they can introduce chemical stressors into aquatic ecosystems. Chlorpyrifos (CPF) is a widely used organophosphate insecticide that can enter aquatic environments and poses potential risks to early-life-stage fish. Because the retina is an extension of the central nervous system and vision-guided behaviors are highly sensitive to neural dysfunction, we hypothesized that CPF exposure disrupts neurobehavioral and visual function via oxidative stress and PPARα-related signaling. Zebrafish larvae were exposed to CPF (0.01, 0.1, 1, 10, and 100 μg/L) with a vehicle control (VC). During the photomotor response assay, exposure to 100 μg/L CPF reduced overall swimming activity by 48.90% and dark-period activity by 57.71%, whereas 1 μg/L CPF modestly increased total distance by 6.96% (p = 0.003) and dark-period distance by 5.40% (p = 0.011). Transcriptomic profiling highlighted nervous- and vision-related functional categories, and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment implicated pathways including gonadotropin-releasing hormone (GnRH), mitogen-activated protein kinase (MAPK), and peroxisome proliferator-activated receptor (PPAR) signaling. Targeted neurotransmitter metabolomics showed significant increases in dopamine, γ-aminobutyric acid (GABA), and acetylcholine across treatment groups, indicating broad neurotransmitter dysregulation. Consistent with these findings, neuronal fluorescence in Tg (elavl3: EGFP) larvae decreased by 12.1% and 32.5% in the 1 and 100 μg/L groups, respectively (p < 0.001), and glial fibrillary acidic protein (GFAP) immunofluorescence increased in the eye/brain/olfactory bulb at 1 μg/L (p = 0.037) and 100 μg/L (p = 0.002). Histology further showed retinal injury, with a 14.3% reduction in photoreceptor layer thickness at 100 μg/L (p = 0.034). Mechanistically, coexposure to a PPARα antagonist (GW6471) alleviated CPF-induced behavioral deficits (1.80-fold increase in dark locomotion) and reduced elevated GABA and dopamine levels by 36.8% and 47.3%, respectively. Together, these results indicate that CPF can impair neuro-visual development and that oxidative stress and PPARα-related signaling are closely associated with these effects.