ESTROGEN INFLUENCES ON NEUROENDOCRINE AGING

生殖老化的特征是雌激素水平的变化;然而，大脑本身也会发生与年龄相关的变化，其中一些可能是雌激素水平改变的结果，而另一些可能是雌激素无关的。因此，本研究将探讨雌激素与下丘脑神经元在生殖衰老过程中的相互作用。研究将侧重于雌激素对促性腺激素释放激素（GnRH）神经元（调节生殖轴的关键细胞）的调节，以及通过NMDA受体作用的促性腺激素能神经元对雌激素对GnRH神经元的影响的介导。为了更好地表征雌激素和下丘脑衰老的作用以及它们的相互作用，将在有或没有雌激素替代的卵巢切除术（OVX）的实验模型以及卵巢完整动物的天然模型中，在生殖功能和内源性雌激素水平的不同阶段进行研究。具体目标1和2将研究雌激素对年轻、中年（MA）和老年Sprague-Dawley OVX大鼠衰老过程中下丘脑功能的影响机制，给予长期或短期雌激素或溶媒替代（Aim 1）或卵巢完整的年轻、MA和老年大鼠发情周期（Aim 2）。对于目标2，在排卵前GnRH/LH激增的当天，在具有高雌激素水平的动情前期，或在雌激素水平低的动情间期I，使用动物。无周期大鼠将在持续发情（高雌激素）或持续发情（高雌激素）或持续间情（低雌激素）时使用。在这两个目标中，雌激素对GnRH和NMDA受体亚单位mRNA和蛋白质的影响将分别通过RNA酶保护试验和蛋白质印迹法定量。将确定GnRH神经元上NMDA受体亚单位的定位，以及它们受雌激素和衰老的调节。还将评估GnRH神经分泌系统对NMDA受体激动剂给药的反应性。具体目标3和4将使用具有28天月经周期的恒河猴作为实验模型，研究下丘脑神经元的雌激素调节的生理变化。目的3：研究去卵巢的幼龄和老龄猴在长期或短期雌激素替代治疗的情况下，下丘脑GnRH和谷氨酸释放的变化，以及NMDA受体激活对GnRH释放的调节作用。目标4将在高雌激素（卵泡期晚期）或低雌激素（黄体期晚期）期间的整个自然月经周期中，对卵巢完整的年轻和年老恒河猴进行类似的测量;将与闭经的年老猴进行比较。预计实验将提供深入了解绝经期雌激素缺乏的神经生物学影响。

Reproductive aging is characterized by changes in estrogen levels; however, the brain itself is subject to age-related changes, some of which may be consequences of altered estrogen levels, and others which may be estrogen-independent. Therefore, the present proposal will examine the interactions of estrogen with hypothalamic neurons in the brain during reproductive senescence. Studies will focus on estrogen regulation of gonadotropin-releasing hormone (GnRH) neurons, the key cells regulating the reproductive axis, as well as the mediation of estrogen's effects on GnRH neurons by glutamatergic neurons, acting via the NMDA receptor. In order to better characterize effects of estrogen and hypothalamic aging, as well as their interactions, studies will be performed in the experimental model of ovariectomy (OVX), with or without estrogen replacement, as well as the natural model of ovarian- intact animals, at different stages of reproductive function and endogenous estrogen levels. Specific Aims 1 and 2 will investigate mechanisms for estrogen's effects on hypothalamic function during aging in young, middle-aged (MA) and old Sprague-Dawley OVX rats, given long-term or short-term estrogen or vehicle replacement (Aim 1) or in ovarian-intact young, MA and old rats during the estrous cycle (Aim 2). For Aim 2, animals are utilized on pro-estrus the day of the pre-ovulatory GnRH/LH surge, with high estrogen levels, or on diestrus I, a day of low estrogen levels. Acyclic rats will be utilized on persistent estrus (high estrogen) or persistent estrus (high estrogen) or persistent diestrus (low estrogen). In both of these aims, effects of estrogen on GnRH and NMDA receptor subunit mRNAs and proteins will be quantitated by RNase protection assay and Western blots, respectively. The localization of NMDA receptor subunits on GnRH neurons, and their regulation by estrogen and aging, will be determined. The responsiveness of the GnRH neurosecretory system to administration of an NMDA receptor agonist will also be assessed. Specific Aims 3 and 4 will investigate the physiological changes in estrogen regulation of hypothalamic neurons, using the rhesus monkey, with its 28 day menstrual cycle, as an experimental model. Aim 3 will examine changes in hypothalamic GnRH and glutamate release and the regulation of GnRH release by NMDA receptor activation in OVX young and old monkeys, with or without long-term or short-term estrogen replacement. Aim 4 will make similar measurements in ovarian-intact young and old rhesus monkeys across the natural menstrual cycle during periods of high estrogen (late follicular phase) or low estrogen (late luteal phase); comparisons will be made with amenorrheic aged monkeys. Experiments are anticipated to provide insight into the neurobiological effects of an estrogen deficiency at menopause.