Effects of polystyrene microplastics and nanoplastics on the hypothalamic-pituitary-testicular axis of Japanese quail

The plastics pollution becomes a global environmental issue with both microplastics (MPs) and nanoplastics (NPs) pose a great risk to animal health. Therefore, we tried to determine the impacts of MPs and NPs on reproductive health of a farm poultry species-Japanese quail (Coturnix japonica) from the perspective of the regulation of hypothalamic-pituitary-testicular (HPT) axis. One-week chicks were exposed to environmental relevance concentration of 0.4 mg/kg and 8 mg/kg polystyrene MPs and polystyrene NPs respectively for five weeks. The results showed MPs and NPs accumulated in the brain and testis in a dose-dependent manner, associated with disruption of both the blood-brain barrier and the blood-testis barrier. Moreover, MPs and NPs exposure caused histopathological injury to the hypothalamus, pituitary and testis resulting in oxidative stress leading to testicular necroptosis and increasing sperm deformity, which induced the decrease of Gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH) and testosterone (T) implying HPT axis disruption and reproductive dysfunction. Furthermore, transcriptome analysis showed that GnRH signaling pathway and steroid hormone biosynthesis pathway were disturbed in the testis. These findings confirmed the adverse influence of MPs and NPs on avian reproductive health and underscored the urgency and necessity of mitigating MPs and NPs impacts.