Broflanilide induces zebrafish neurobehavioral defects by interfering with synaptic homeostasis

Broflanilide is a novel bisamide insecticide that is extensively used. Previous study reported that broflanilide induced neurotoxicity during zebrafish embryonic development, however, its behavior impact and the involved neural cell heterogeneous mechanism remains largely unknown. Here, we performed a series of neuro-behavior test for adult zebrafish that were exposed to 5 and 25 μg/L broflanilide for 30 days. We found that 25 μg/L broflanilide could induce abnormal locomotion and cognitive defect. These changes were accompanied by synaptic homeostasis inference (decreased number of synaptic knobs), and neuron loss. Simultaneously, a targeted metabolomic assay showed that the glutathione metabolism and GABAergic synapses in brain were significantly altered, indicating an altered synaptic transmission, which is consistent with the synaptic injury. Single-cell RNA sequencing of zebrafish brain showed changed cell composition after exposure, including a decreased ratio of neuron and oligodendrocyte, and an increased proportion of astrocytes. Meanwhile, genes involved in synaptic functional pathways were altered in neuron, astrocyte and oligodendrocytes, which partly explained the disruption of synaptic homeostasis. These findings reveal the long-term risk of broflanilide toward neural health of aquatic organisms and suggest an across-cell types transcriptional regulation in mediating the neurotoxicity.