ESTROGEN REGULATED PLASTICITY OF HIPPOCAMPAL NEURONS

为了充分了解大脑功能在衰老过程中的变化，有必要了解随着年龄增长而下降的激素，如雌二醇（E）和脱氢表雄酮（DHEA）如何维持成人大脑的正常可塑性和弹性。关于认知能力下降和阿尔茨海默病，雌二醇是研究得最好的激素;然而，即使如此，我们在很大程度上也不知道衰老的大脑如何在细胞和解剖学水平上对雌二醇做出反应，或者雌二醇（和脱氢表雄酮）是否具有与其调节可塑性的能力相关的神经保护作用。本项目利用胚胎海马神经元的细胞培养，使其在体外成熟至少10天，以分化并建立神经元与神经胶质细胞环境之间的连接。它不仅使用细胞培养，免疫细胞化学和原位杂交，而且还采用差异显示技术来识别在诱导恢复力和突触形成过程中被激活的新的和已知的基因。该项目有三个目标：第一，在细胞和分子水平上研究雌二醇（E）引起海马神经元突触形成的过程;这将与本方案项目其他部分正在研究的老龄大鼠和灵长类动物大脑中E诱导的海马突触形成与年龄有关的假设下降的研究有关;其次，研究导致突触形成的E治疗条件如何改变海马对兴奋性毒性损伤的反应，并且，在这方面，第三，研究另一种随着年龄增长而下降的类固醇可能的协同神经保护作用，脱氢表雄酮（DHEA）。据报道，DHEA可以阻断NMDA诱导的兴奋性毒性，至少部分是通过作用于神经胶质细胞来实现的，神经胶质细胞也对雌激素有反应。神经胶质细胞也参与E诱导的突触形成，这些研究中获得的信息也将阐明这方面的问题。

In order to fully understand changes in brain function during aging, it is necessary to understand how hormones that decline with age, such as estradiol (E) and dehydroepiandrosterone (DHEA) maintain the normal plasticity and resilience of the adult brain. Estradiol is the best studied hormone with respect to cognitive decline and Alzheimer's disease; yet, even then, we are largely ignorant about how the aging brain responds to E at the cellular and at anatomical levels, or whether E (and DHEA) have neuroprotective actions that are related to their ability to regulate plasticity. This project utilizes cell culture of embryonic hippocampal neurons that are allowed to mature for at least 10d in vitro to differentiate and establish connections among neurons with an environment of glial cells. It uses not only cell culture, with immunocytochemistry and in situ hybridization, but also employs the technique of differential display to identify novel and known genes that are activated during the induction of resilience and synapse formation. The project has a three-fold objective: First, to study the processes at the cellular and molecular level by which estradiol (E) causes synapse formation in hippocampal neurons; this will be relevant to the studies of the hypothesized age-related decline in E- induced hippocampal synapse formation in the aging rat and primate brain which are being studied in other components of this program project; Second, to study how the conditions of E treatment that results in synapse formation alter the response of the hippocampus to excitotoxic damage, and , in this connection, Third, to investigate the possible synergistic neuroprotective effects of another steroid that declines with age, dehydroepiandrosterone (DHEA). DHEA has been reported to block NMDA-induced excitotoxicity and to do so, at least in part, by acting on glial cells, which are also responsive to estrogens. Glial cells also participate in E-induced synapse formation and the information gained in these studies will illuminate this aspect as well.