Aromatization in Brain and Pituitary: Regulation of Reproduction in Vertebrates

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Circulating androgen derived from gonadal secretions is converted to estradiol (neuroestrogen) within the brain and pituitary. This transformation, which is catalyzed by an enzyme complex termed aromatase (P450arom), is essential for the full expression of androgen actions on brain sex differentiation, sex behavior and reproductive neuroendocrinology. Because the brain and pituitary are structurally and functionally complex and the quantity of neuroestrogen is very small, it has been difficult to determine how P450arom is regulated, its precise cellular and subcellular location, and the cellular targets and mechanisms by which neuroestrogen exerts its actions. Dr. Callard has identified an animal model, the goldfish, in which P450arom activity is 100-to-100- times higher than in conventional laboratory species. Moreover, brain androgen receptors are correspondingly elevated. Based on this correlation and results of experiments during the last project period, she postulates a functional interrrelationship between P450arom and androgen receptors in which locally synthesized estrogen acts as a positive feedback regulator of quantifiable endpoints for elucidating the parahormonal role of neuroestrogen in brain and pituitary. To this end, she proposes to isolate and characterize cDNA probes for the goldfish P450arom and androgen receptor genes, to develop antibodies for measuring their protein products, and to apply these new tools to unanswered questions using the goldfish model.