It is well known that the brain undergoes changes in a sexually dimorphic manner during fetal development. Here, we postulate that sex differences are present in another neuroendocrine tissue, the pituitary gland. We tested the hypothesis that androgens mediate sex differences in gonadotropin gene expression during fetal development of the anterior pituitary gland. We compared gonadotropin gene expression in fetal male and female mice treated with either an androgen receptor agonist or antagonist from embryonic day 15.5-17.5. Multiple gonadotrope-derived genes were expressed at significantly higher levels in females compared to males, including luteinizing hormone beta (Lhb), follicle-stimulating hormone beta (Fshb) and gonadotropin-releasing hormone receptor (Gnrhr). Treatment with flutamide, testosterone, or dihydrotestosterone eliminated the sex difference in gene expression. Specifically, flutamide relieved the suppression in male gene expression to the level observed in females. In contrast, testosterone and dihydrotestosterone attenuated female gene expression to male levels. Having determined that male and female fetal pituitary glands contain an equivalent number of gonadotrope cells, we focused on understanding the mechanism underlying sex-dependent transcriptional regulation within this cell type. Fetuses either lacking GnRH or GnRH receptor showed no sex difference in expression of Lhb, Fshb, or Gnrhr, suggesting that GnRH signaling is important for expression in a sex-dependent manner. Collectively, our data demonstrate that there is a sex difference in gonadotropin gene expression during fetal development which is regulated by androgens. Furthermore, we postulate that hypothalamic drive to the pituitary is greater in female fetuses and blunted in males during fetal development.

Stress is a condition experienced by all living organisms. Stress can initiate psychological and physiological responses that may inhibit other systems in the body, including the reproductive system. Infertility is a concern for many individuals, and previous research has found a correlation between infertility and stress. In the mouse model, stress can inhibit normal reproductive function; however, the neural mechanisms mediating this phenomenon are not yet fully understood. The paraventricular nucleus (PVN) is a key region activated during the response to stress and this nucleus contains corticotropin releasing hormone (CRH) neurons. Evidence supports a CRH receptor type 2 pathway to play a key role in stress-induced suppression of reproductive function. Therefore, we hypothesized that urocortin 2 (UCN2), a neuropeptide in the CRH family with high affinity for CRH receptor type 2, may be a good candidate for a mediator of stress-induced suppression of the LH surge. We observed that central administration of UCN2 was sufficient to block an estradiol-induced LH surge. Next, we looked upstream at a population of norepinephrine (NE) producing neurons in the A2 region of the nucleus of the solitary tract in the brainstem. The A2NE population is known to be activated during a variety of stress types, and ablation of this population restores reproductive function in a hypoglycemic stress model. We hypothesized that this population was involved in stress induced reduction of reproductive function, and we observed that chronic activation of the A2NE population was sufficient to inhibit estrous cyclicity. In summary, these data support a working model whereby A2NE neurons can activate UCN2 cells in the PVN and initiate reproductive suppression during stress.