Reproductive aging & long-term hormone replacement therapy in the rhesus macaque
Menopause is a natural transition heralded by the cessation of menstrual cycles and ovulation, and it occurs in all women at an average of about 50 years of age. While not a disease, menopause is often accompanied by symptoms that interfere with the quality of life and these symptoms are due to the relatively abrupt deprivation of E2 and P4 experienced during reproductive aging. Reproductive aging consists of changes in the synthesis and release of hormones from the hypothalamus, pituitary and gonad, which make up the HPG axis. Because gonadal hormones play critical roles in many systems throughout the body and brain, not just reproduction, treatment of menopausal symptoms to date largely involves hormone replacement therapy (HRT) with E2, P4 or their combination. While not intended to treat other neurobiological symptoms beyond hot flushes, HRT has the potential to exert widespread actions due to the abundance of hormone receptors throughout the nervous system. Thus, a fuller understanding of the neurobiology of menopause is badly needed. Although much of the research into the mechanisms that underlie reproductive aging focuses on ovarian failure and follicular atresia (cell death), there is evidence that there are significant alterations in the function of the neuroendocrine levels - the hypothalamus and pituitary - that also contribute to this process. As the mean age of the population increases, the number of post-menopausal women continues to grow with broad economic, healthcare and social costs. It is increasingly important to understand the complex mechanisms underlying reproductive aging and the effects of HRT. In this dissertation, I focus on the question of how the female non-human primate hypothalamus changes both with aging and in response to steroid hormone treatments.