Acute toxicity of broflanilide on neurosecretory system and locomotory behavior of zebrafish (Danio rerio)

Broflanilide, a novel meta-diamide insecticide, possesses moderate acute toxicity to zebrafish, with a 96-h median lethal concentration (96-LC50) of 0.76 mg/L. However, its effect on fish behavior and the underlying mechanisms are still unclear. The present study evaluated the effects of broflanilide on the zebrafish brain over a 96-h exposure by comparing the histopathological changes and relative expression of targeted genes with the behavioral metrics. The results of the toxicity test showed that broflanilide could cause deformities, such as deformation of the operculum and spinal curvature, at 0.6, 0.82 and 1.15 mg/L. Results also showed tissue damage and apoptosis in the cerebellum under 0.27 and 0.6 mg/L exposure. Additionally, broflanilide affected the neurotransmitters, metabolites and transcripts of genes associated with dopamine, gamma-aminobutyric acid expression. and the signaling pathways in zebrafish brains at 0.60 mg/L after 1 h and 96 h of exposure, while the levels of glutamate, glutamate decarboxylase, GABA transaminase, nicotinamide adenine dinucleotide (NADH) and adenosine triphosphate (ATP) were also inhibited at 0.27 mg/L after 96 h of exposure. The accumulated swimming distance was significantly longer and the average speed was significantly faster than the control at 0.27 and 0.6 mg/L after 1-h of exposure, while these metrics were lowered at 0.6 mg/L after 96 h of exposure. The study results demonstrates that broflanilide affects the zebrafish brain, neurotransmitters and associated fish behaviors. This study also provides deeper insight into the mechanistic understanding of the effects of broflanilide on the zebrafish brain.