The overall goal of this proposal is to upgrade our understanding of the primate neuroendocrine reproductive axis, and thereby to lay a foundation for the development of novel contraceptives and to gain new insights about the etiology of idiopathic human reproductive disorders. This goal is thus responsive to one of NICHD's new Research Priorities: ?To Encourage the Development of Innovative Technologies and Model Systems to Study Fertility and Infertility.? Specifically, the proposed research will empirically test the hypothesis that active immunization against GnRH-II can provide safe and effective long-term contraception - by selectively silencing the LH surge mechanism, while leaving the rest of the neuroendocrine reproductive axis intact. In humans, gonadotropin-releasing hormone (GnRH) neurons represent the primary neuroendocrine link between the brain and the rest of the reproductive axis, yet the mechanism by which these neurons trigger ovulation is poorly understood. Recently, however, human and rhesus macaques (but not rodents) were found to express two different molecular forms of GnRH (GnRH-I and GnRH-II). Furthermore, only the GnRH-II neurons were found to respond positively to estrogen feedback, suggesting that GnRH-II neurons serve as the primary trigger of the mid-cycle preovulatory LH surge. We therefore hypothesize that selective silencing of GnRH-II neurons will block ovulation without perturbing ovarian steroidogenesis or affecting negative feedback of estrogen on GnRH-I neurons. This hypothesis will be empirically tested using the female rhesus macaque, a highly translational nonhuman primate animal model that shows human-like menstrual cycles and similar organization of its reproductive neuroendocrine axis.
Specific Aim 1 : To test the hypothesize that active immunization against GnRH-II will selectively block ovulation without impacting ovarian steroidogenesis. We will test this hypothesis by immunizing adult female rhesus macaques against unique non-conserved regions of the GnRH-II neuropeptide; control animals will be immunized against a unique non-conserved region of GnRH- I. After immunization, the animals will be examined daily for signs of menstruation and circulating levels of reproductive hormones (i.e., LH, FSH, estradiol, progesterone, anti-Mllerian hormone) will be monitored in bi- weekly blood samples. We expect to show that selective immunization against GnRH-II will block development of the mid-cycle LH surge and corpus luteum formation (i.e., inferred by maintenance of low circulating progesterone levels).
Specific Aim 2 : To elucidate the neuroendocrine mechanism that underlies the contraceptive potential of GnRH-II silencing. Using remote serial blood sampling we will examine the dynamic relationships between reproductive hormone levels in the circulation after immunization (1) in ovary-intact animals, (2) after ovariectomy, and (3) after estrogen induction of an LH surge. We expect to show that selective silencing of GnRH-II will completely block the positive estrogen feedback component of the neuroendocrine reproductive axis, while leaving the GnRH-I-mediated negative feedback component functionally intact.
There is compelling evidence that the hypothalamus of humans and nonhuman primates produces two different molecular forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II). Furthermore, expression of GNRH-II, but not GNRH-I, increases markedly in direct response to estrogen, suggesting that GnRH-II neurons serve as the primary trigger of the mid-cycle preovulatory LH surge. Using the rhesus macaque as a translational animal model, we will empirically test the hypothesis that active immunization against GnRH-II can provide safe and effective long-term contraception - by selectively silencing the LH surge mechanism, while leaving the rest of the neuroendocrine reproductive axis intact.
