Sexual behavior dysfunction and sickness behavior as an early warning indicators of imidacloprid exposure, associated with pituitary–adrenal axis dysregulation and DNA damage in Japanese quails

IntroductionJapanese quails (Coturnix coturnix japonica) serve as vital models in behavioral neuroendocrinology and ecotoxicology, particularly for understanding the neuroendocrine pathways regulating avian mating strategies. Subchronic exposure to neonicotinoid insecticides poses critical threats to avian reproduction and population dynamics.MethodsThis study comprehensively evaluated the neuroendocrine, behavioral, morphometric, and genotoxic impacts of chronic oral imidacloprid (IMI) exposure in Japanese quail (Coturnix coturnix japonica) across developmental and adult stages (weeks 7–12 of age).ResultsImidacloprid administration significantly delayed pubertal onset and increased body weight at sexual maturity in both sexes (p ≤ 0.003). Morphometric analysis revealed profound somatic and gonadal hypotrophy, evidenced by persistent reductions in the brain-somatic index (BSI) and gonado-somatic index (GSI; testicular and ovarian masses) across development (p < 0.0001). Endocrine profiling demonstrated systemic disruption of the hypothalamic–pituitary–gonadal (HPG) axis, marked by significant suppression of circulating anterior pituitary gonadotropins (FSH and LH), testosterone, progesterone, and total estrogens (p < 0.0001), alongside biphasic 17β-estradiol deregulation. Behaviorally, exposed birds exhibited pronounced hypodipsia, increased stationary crouching, and progressive sickness behavior (p < 0.001). In males, IMI induced severe reproductive and behavioral deficits, characterized by marked reductions in cloacal gland area (304.66 vs. 332.90 mm), relative testis mass, and merocrine foam production (p < 0.001), accompanied by significant suppression of appetitive courtship displays (chasing, waltzing, wing flapping) and consummatory copulatory performance (mounting, cloacal contact movements, libido scores, and copulatory efficiency) in both rearing cages and standard testing arenas (p < 0.05 to p < 0.0001). In females, IMI significantly blunted proceptive squatting and holding-still compliance scores during mounting encounters without altering running escape frequency, alongside severe reductions in total weekly egg production, egg weight, hen-day egg production, and total egg mass (p < 0.001). Furthermore, the alkaline comet assay revealed marked hepatic and cerebral genomic DNA damage, with significant elevations in percentage DNA damage and tail moment (p < 0.05 to p < 0.001).ConclusionOverall, these findings demonstrate that chronic imidacloprid exposure induces multi-level neuroendocrine disruption, systemic genotoxicity, and severe reproductive failure in avian models, highlighting significant ecotoxicological risks to non-target avian species.