A comparison of aromatase, 5α‐, and 5β‐ reductase activities in the brain and pituitary of male and female quail (C. c. japonica)

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Abstract
In numerous vertebrate species including Japanese quail (Co-turnix coturnix japonica), actions of testosterone (T) on neuroendocrine target tissues are mediated in part by conversion to estrogenic and androgenic metabolites. In order to assess which pathways were favored in each identified androgen target area in quail brain and whether there were discernible sex differences, we developed an assay for simultaneously quantifying aromatase, 5α-, and 5β-reductase. In addition, we made the first definitive identification of aromatase in quail pituitary and compared all three enzyme activities in the pituitary of males and females. Enzymes were measured in tissue homogenates by the conversion of [3H]androstenedione to [3H]estrone, [3H]5α-androstanedione, and 5β-androstanedione. Aromatase activity was restricted to limbic tissues (anterior hypothalamus > posterior hypothalamus > septum > archistriatum containing nucleus taenia) while hyperstriatum, cerebellum, and midbrain containing nucleus intercollicularis were aromatase-negative. Quail pituitary aromatized androgen at rates equivalent to anterior hypothalamus pre-optic area (aHPOA). 5α- and 5β-reductase were present in all tissues tested. Aromatase was significantly higher in aHPOA and pituitary of males, whereas 5α-reductase was significantly higher in female pituitary. These data suggest that a complex of androgen-metabolizing enzymes controls the neuroanatomic (spatial) distribution of active hormone in neuroendocrine tissues and that quantitative differences between males and females may account for sex differences in behavior.