ESTROGEN REGULATED PLASTICITY OF HIPPOCAMPAL NEURONS

为了充分了解衰老过程中大脑功能的变化，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）是如何维持成人大脑正常的可塑性和弹性的。雌二醇是在认知能力下降和阿尔茨海默病方面研究得最好的激素；然而，即便如此，我们对衰老的大脑如何在细胞和解剖水平上对E做出反应，或者E（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，仍知之甚少。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10d，在神经胶质细胞环境中分化并建立神经元之间的连接。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弹性和突触形成过程中激活的新基因和已知基因。该项目有三个目标：首先，在细胞和分子水平上研究雌二醇(E)导致海马神经元突触形成的过程；这将与在衰老的大鼠和灵长类动物大脑中E诱导的海马突触形成的假设与年龄相关的下降有关，该研究正在该项目的其他组成部分中进行研究；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，在这方面，第三，研究另一种随年龄下降的类固醇脱氢表雄酮（DHEA）可能的协同神经保护作用。据报道，脱氢表雄酮可以阻断nmda诱导的兴奋性毒性，至少在一定程度上是通过作用于神经胶质细胞来实现的，而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，这些研究获得的信息也将阐明这方面。

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.