Central Actions of Estrogens: Effects on GnRH neurons

雌激素对中枢神经系统的细胞功能和存活有多种影响。这项拟议的研究探索了雌激素控制促性腺激素释放激素(GnRH)神经元的部位和机制。这些神经元形成了中央调节生育能力的最终共同途径；因此，它们的适当功能对脊椎动物物种的生存至关重要。根据暴露水平和持续时间的不同，雌激素可以抑制(负反馈)或刺激(正反馈)GnRH释放。女性生殖周期的特点是在负反馈和正反馈之间进行自然切换，这对启动排卵过程至关重要。负反馈、正反馈以及这些模式之间的切换是如何带来的，目前还不得而知。这种生理现象，加上其输入的相对简单和已知的雌激素对GnRH分泌输出的影响，使GnRH神经元成为一个有趣的模型，用于研究多种中枢雌激素作用是如何整合在一起产生反应的。电生理、分子和细胞生物学方法将被用来研究绿色荧光蛋白标记的活的GnRH神经元。在发情周期和急性接触类固醇后，将在负反馈和正反馈的生理模型中研究雌激素的影响。工作假说是，雌激素在两个部位反馈调节GnRH的释放：通过雌激素敏感的传入和直接在GnRH神经元上跨突触；在每个部位，两种类型的信号机制被激活：基因组和非基因组。目标1将确定雌激素如何影响GnRH神经元的离子型突触输入。目的2研究雌激素对促性腺激素释放激素神经元的内源性电导、兴奋性和放电模式的影响。目的3研究雌激素激活促性腺激素释放激素神经元的信号机制，探讨雌激素对促性腺激素释放激素神经元中影响细胞兴奋性的蛋白编码基因表达的影响，以及雌激素引起的激酶级联反应所介导的非基因组作用。从这三个目的获得的实验数据将扩大我们对雌激素通过不同机制和不同部位的作用如何整合到影响生殖的理解，揭示GnRH神经元正反馈和负反馈调节的机制差异。从这些研究中获得的知识将促进在人类、家畜和濒危野生物种中开发新的合理的生育控制策略，并可能适用于了解雌激素对更复杂的神经系统(如海马体和皮质)的作用。

Estrogens have multiple effects on cell function and survival in the central nervous system. The proposed research explores the sites and mechanisms through which estrogens control gonadotropin-releasing hormone (GnRH) neurons. These neurons form the final common pathway for central regulation of fertility; their proper function is thus critical to survival of vertebrate species. Depending on level and duration of exposure, estrogen can inhibit (negative feedback) or stimulate (positive feedback) GnRH release. The female reproductive cycle is characterized by a natural switch between negative and positive feedback that is critical to initiating the ovulatory process. How negative feedback, positive feedback and the switch between these modes are brought about is unknown. This physiological phenomenon combined with the relative simplicity of their inputs and the known effects of estrogen on GnRH secretory output make GnRH neurons an intriguing model for studying how multiple central estrogen actions are integrated to produce a response. Electrophysiological, molecular and cellular biological approaches will be used to study living GnRH neurons tagged with green fluorescent protein. Estrogen effects will be studied in physiological models of negative and positive feedback, during the estrous cycle and after acute exposure to the steroid. The working hypothesis is that estrogen feeds back to regulate GnRH release at two sites: transsynaptic via estrogen-sensitive afferents and directly on GnRH neurons; at each site, two types of signaling mechanisms are activated: genomic and non-genomic. Aim 1 will determine how estrogen acts to affect ionotropic synaptic inputs to GnRH neurons. Aim 2 will examine estrogen- induced changes in intrinsic conductances, excitability and firing pattern of GnRH neurons. Aim 3 will study the signaling mechanisms activated in GnRH neurons by estrogens, exploring estrogen-induced changes in the expression of genes coding for proteins that affect cell excitability in GnRH neurons, as well as non-genomic actions mediated by kinase cascades initiated by estrogen action. Data obtained from experiments in these three Aims will expand our understanding of how estrogen actions via different mechanisms and at different sites are integrated to impact reproduction by revealing mechanistic differences that underlie positive and negative feedback regulation of GnRH neurons. Knowledge gained from these studies will foster development of novel rational strategies for fertility manipulation in humans, domestic animals, and endangered wild species, and may be applicable to understanding estrogen action on more complex neural systems, such as hippocampus and cortex.