Short‐Term Exposure to Benzo(a)Pyrene Causes Disruption of GnRH Network in Zebrafish Embryos

Benzo(a)pyrene (BaP), a polycyclic aromatic hydrocarbon, is considered a common endocrine disrupting chemical (EDC) with mutagenic and carcinogenic effects. In this work, we take advantage of the vertebrate zebrafish model to investigate the effect of the exposure of Bap on the hypothalamo-pituitary-gonadal axis, using the tg(GnRH3:EGFP) reporter line that expresses the green fluorescence protein under the control of the GnRH3 promoter. Zebrafish embryos were treated with 5 and 50nM BaP from 2.5 to 72 hpf and obtained data were compared with those from DMSO-treated controls. We followed the entire development of GnRH3 neurons, starting to proliferate from the olfactory region at 36 hpf, migrating at 48 hpf and then reaching the pre-optic area and the hypothalamus at 72 hpf. Interestingly, we observed a compromised neuronal architecture of the GnRH3 network after the administration of 5 and 50nM BaP, also confirmed by the dose-dependent reduction of GnRH3-GFP positive cells. Given the toxicity of this compound, we evaluated the expression of genes involved in antioxidant activity, oxidative DNA damage and apoptosis and we found an upregulation of these pathways. Consequently, we performed a TUNEL assay and we confirmed an increment of cell death in brain of embryos treated with BaP. In conclusion our data reveal that short-term exposure of zebrafish embryos to BaP affects GnRH3 development likely through a neurotoxic mechanism.