Reduced prepubertal expression of progesterone receptor in the hypothalamus of female aromatase knockout mice. Endocrinology

Previous research using -fetoprotein knockout and aromatase knockout (ArKO) female mice suggested that the developing hypothalamic mechanisms that later control feminine sexual be-havior are protected prenatally fromestradiol, whereas shortly after birth, theymay be stimulated by this same sex hormone. In the present study, we found that the amount of progesterone receptor immunoreactivity (PR-ir) in the anteroventral periventricular nucleus and medial part of the medial preoptic nucleus was significantly lower in ArKO female mice than in wild-type (WT) females at several prepubertal ages including postnatal d 15 (P15), P15, P20, and P25 but not neonatally at P0, P5, or P10. Likewise, PR-ir in the lateral subdivision of the ventromedial hypo-thalamic nucleus was significantly lower at P25 in ArKO vs. WT female mice but not at earlier postnatal ages. PR-ir was consistently higher in male than in female WTmice in the anteroventral periventricular nucleus and medial preoptic nucleus over P0–P10 and in the ventromedial hypo-thalamic nucleus over P0–P20. In these brain regions across these latter ages, PR-ir in male ArKO mice was significantly lower than in WT males and resembled the values seen in WT females, confirming previous reports that estradiol formed in the developing male hypothalamus from testicular testosterone is responsible formale-typical levels of neural PR expression. Thus, estradio