Nonmammalian vertebrate models in studies of brain-steroid interactions

Estrogen formation in brain and pituitary mediates certain androgen actions in central targets. Goldfish (Carassius auratus) and quail (Coturnix coturnix japonica) have been advantageous for studying the role of locally formed estrogen in autoregulating aromatization and in controlling estrogen receptor occupancy, androgen receptor levels, and behavioral expression. Data from these two experimental models reveal a molecular basis for androgen-estrogen synergism in neuroendocrine tissues and for alterations in androgen sensitivity/responsiveness. These mechanisms are essential components of seasonal reproduction in the test species and may have wider relevance for cyclicity in other vertebrates, including mammals.