Expression of steroid hormone receptors in the fetal sheep brain during the critical period for sexual differentiation

The objective of this study was to examine the expression of receptors for androgen, estrogen, and progesterone in the fetal sheep brain during the critical period for sexual differentiation. We isolated mRNA from the hypothalamus-preoptic area (HPOA), amygdala (AMYG), medulla (MD), frontal cortex (FCTX) and olfactory bulbs (OB) of fetal sheep that were delivered on day 64 of gestation. Using a ribonuclease protection assay and species-specific cRNA probes, we measured mRNA expression levels of androgen receptor (AR), estrogen receptor alpha (ERα) and progesterone receptor (PR). ERα and AR mRNA were expressed in all of the tissues tested and highest in the HPOA. PR mRNA was measured in HPOA and AMYG only and was significantly higher in male than in female fetuses. We conclude that the fetal brain is a target site for circulating steroid hormones. These data have implications for the steroid dependent development of sexually dimorphic brain functions in sheep.