Endocrine modulators and sexual differentiation in Japanese quail : With emphasis on the neuroendocrine system

Abstract: Chemical disruption of the endocrine system in various animal species is currently attracting considerable interest, but avian models are not yet widely used in studying endocrine disturbances. This thesis shows the occurrence of alterations in sexual behavior and reproductive organs in adult Japanese quail (Coturnix japonica) following embryonic exposure to estrogen-like chemicals.Exposure to synthetic estrogens and the environmental pollutant o,p´-DDT caused depressed male sexual behavior. Testis weight asymmetry, cloacal gland area and plasma testosterone levels were also changed, albeit not by all compounds. In females, o,p´-DDT caused disturbed egg laying and malformations of the oviducts. The pollutants bisphenol A and tetrabromobisphenol A did not cause estrogen-like effects at the doses tested. Sexual differentiation of the brain in birds is directed by estrogen, and in adult males, sexual behavior is activated by testosterone after local aromatization into estrogen in the brain. Consequently, the expression of estrogen receptors (ERs) is important both during differentiation and for activation of sexual behavior. The localization of ERα and ERβ mRNA in the brain was studied by in situ hybridization in embryos and adults of both sexes. Both receptors were localized in brain areas regulating sexual behavior. No distinct sex differences in localization or density of the mRNAs were found, but ERβ seemed to be present in higher density in the male nucleus taeniae. In embryos, ERβ was detected earlier than ERα, but by the end of incubation, both receptors were shown to be present. In conclusion, it was found that several reproductive variables in adult quail are disturbed by exposure to estrogen-like chemicals during the critical period of sexual differentiation. Sexual behavior was the most sensitive endpoint in males and it is suggested in the thesis that this variable be included in avian in vivo testing for endocrine modulating chemicals. In females, functional and morphological changes of the oviducts are useful endpoints for estrogen-like effects. The roles of ERα and ERβ in normal sexual differentiation in birds and in chemically induced disruptions of this process need to be elucidated further.