Steroid profiles in quail brain and serum: sex and regional differences and effects of castration with steroid replacement

Abstract

Both systemic and local production contribute to the concentration of steroids measured in the brain. This idea was originally based on rodent studies and was later extended to other species including humans and birds. In quail, a widely used model in behavioral neuroendocrinology, it was demonstrated that all enzymes needed to produce sex steroids from cholesterol are expressed and active in the brain but the actual concentrations of steroids produced were never investigated. We carried out a steroid profiling in multiple brain regions and serum of sexually mature male and female quail by gas chromatography coupled to mass spectrometry. Concentrations of some steroids (e.g., corticosterone, progesterone, testosterone) were in equilibrium between brain and periphery but other steroids (e.g., pregnenolone, 5α/β‐dihydroprogesterone and estrogens) were more concentrated in the brain. In brain regions investigated, pregnenolone sulfate, progesterone and estrogen concentrations were higher in the hypothalamus‐preoptic area (POA). Progesterone and its metabolites were more concentrated in the female than the male brain while testosterone, its metabolites and dehydroepiandrosterone (DHEA) were more concentrated in males suggesting that sex steroids present in quail brain mainly depend on their specific steroidogenic pathways in ovaries and testes. However, castration experiments suggested that sex steroids could also be produced in the brain independently of peripheral source. Treatment with testosterone or estradiol restored the concentrations of most androgens or estrogens, respectively, although penetration of estradiol in the brain appeared more limited. These studies illustrate the complex interaction between local brain synthesis and the supply from the periphery for the steroids present in the brain that are either directly active or represent the substrate of centrally located enzymes.

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