Estrogen and hippocampal plasticity

描述(由申请人提供)：妇女健康倡议(WHI)在2003-2004年间报告称，激素替代疗法，无论是黄体酮和雌激素联合治疗，还是单独使用雌激素，对绝经后妇女的心血管或认知都没有好处。这些结论导致数百万女性退出激素替代疗法。然而，流行病学研究中观察到的明显益处已经启动了对WHI研究的关键重新评估。潜在的冲突包括马结合激素的使用，激素缺乏的持续时间，以及受试者的高龄。越来越明显的是，激素替代对维持心血管和认知健康都有好处，这一点变得越来越明显。不幸的是，我们对为什么E2替代可能或不可能挽救认知缺陷的理解受到了细胞水平上关于E2如何替代的机制信息的不足的阻碍 调节突触功能。因此，临床数据中的差异只有通过进一步研究E2的基本作用机制才能得到解决。由于所有女性都经历更年期，并在这种状态下度过了近三分之一的生命，因此必须致力于密集的研究努力，以获得新的知识，为维持心理和认知健康的干预措施提供洞察力。在海马CA3-CA1突触，雌二醇(E2)增加了脊椎密度、NMDAR传递和LTP5-8，这些机制被认为是增强记忆的基础。然而，目前尚不清楚脊柱密度增加与LTP之间是否存在功能关系。这一点很重要，因为在老年动物中，E2增加了NMDAR的表达，但不增加脊柱密度，这可能解释了与年龄相关的E2替代疗法认知益处的下降。另一方面，老年动物可能能够在没有新突触生长的情况下增加可塑性。从内嗅皮层到CA1细胞的皮质输入是否类似于CA3-Schaffer侧支突触受E2的调节也是未知的。知道这一点很重要，因为这些突触在空间探索过程中驱动CA1细胞，而雌二醇增加空间记忆。众所周知，E2需要胆碱能神经支配来增强记忆，但尚不清楚突触功能的增加是否也是如此。因为E2保护胆碱能细胞免于退化，在更年期丢失E2可能会导致胆碱能细胞死亡增加。这一点很重要，因为绝经后的女性比男性患阿尔茨海默氏症的风险更大，而E2的替代降低了这种风险。因此，胆碱能传递不足将限制雌二醇产生认知益处的能力。最后，还没有研究调查长期的激素丢失对E2诱导突触功能变化的能力的影响。只有一项研究调查了NMDAR mRNA水平的潜在变化，但没有观察到显著的结果。这具有很高的临床重要性，因为确定机会之窗及其与实际年龄的关系对于进一步了解激素替代疗法的有效性是绝对必要的。在这个方案中，我们将使用细胞外树突状体场电位和全细胞膜片钳记录技术，在幼年、中年和老年卵巢切除(OVX)雌性大鼠用雌二醇或赋形剂处理的急性切片的CA1区，以追求以下特定目的：目标1将验证E2通过增加表达NMDAR的沉默突触的密度来增加LTP的幅度的假设 包含NR2B亚基；AIM 2将检验E2介导的脊柱密度和 突触功能不仅限于Schaffer侧支通路，还包括内嗅觉皮质和CA1锥体细胞远端树突之间的突触；AIM3将测试以下假设：胆碱能去神经将阻止E2诱导的脊髓密度、NMDAR传递和LTP幅度的增加，但来自颈上神经节的交感出芽将修复这些缺陷；AIM 4将测试该假设，即长期的激素丢失结合正常衰老阻止了E2替代诱导CA3-CA1突触的形态和功能变化的能力。

DESCRIPTION (provided by applicant): The Women's Health Initiative (WHI) reported in 2003-2004 that hormone replacement therapy, either progesterone and estrogen in combination or estrogen alone, provided no cardiovascular or cognitive benefit in postmenopausal women. These conclusions lead millions of women to withdraw from hormone replacement therapy. However, clear benefits observed in epidemiological studies have initiated a critical reevaluation of the WHI study. Potential conflicts include the use of equine conjugated hormones, the duration of hormone deficiency, and the advanced age of the subjects. It is becoming increasingly obvious that there is a "window of opportunity" in which hormone replacement is beneficial for maintaining both cardiovascular and cognitive health. Unfortunately, our understanding of why E2 replacement may or may not rescue cognitive deficit is hindered by insufficient mechanistic information at the cellular level regarding how E2 modulates synaptic function. Thus, the discrepancy in the clinical data will only be resolved by further investigation into the basic mechanisms through which E2 acts. Because all women undergo menopause and spend nearly 1/3 of their life in this state, intensive research effort must be dedicated to obtaining new knowledge that will provide insight for interventions to sustain mental and cognitive health. At hippocampal CA3-CA1 synapses, estradiol (E2) increases spine density, NMDAR transmission, and LTP5-8, mechanisms believed to underlie the enhanced memory. However, it remains unknown whether there is a functional relationship between the increased spine density and LTP. This is important because in aged animals, E2 increases NMDAR expression but not spine density, which may explain the age related decrease in cognitive benefit of E2 replacement therapy. On the other hand, aged animals may be able to increase plasticity without the growth of new synapse. It is also not known whether the cortical input onto CA1 cells from the entorhinal cortex is modulated by E2 similarly to CA3 Schaffer collateral synapses. This is critical to know because these synapses drive CA1 cells during spatial exploration and estradiol increases spatial memory. It is known that E2 requires cholinergic innervation to enhance memory, but is it not known whether the same is true for the increase in synaptic function. Because E2 protects cholinergic cells from degeneration, loss of E2 in menopause could lead to increased cholinergic cell death. This is significant because post menopausal women are at greater risk of developing Alzheimer's disease than men and E2 replacement decreases this risk. Therefore insufficient cholinergic transmission would limit the ability of E2 to cause cognitive benefit. Finally, no study has investigated the impact of prolonged hormone loss on the ability of E2 to induce changes in synaptic function. Only one study has investigated potential alterations in NMDAR mRNA levels, but no significant results were observed. This is of high clinical importance because determining the window of opportunity and how this relates to chronological age is absolutely essential to further our understanding of the effectiveness of hormone replacement therapy. In this proposal, we will use extracellular dendritic field potential and whole-cell patch clamp recording techniques in area CA1 of acute slices from young adult, middle aged and aged ovariectomized (OVX) female rats treated with estradiol or vehicle to pursue the following Specific Aims: AIM 1 will test the hypothesis that E2 increases the magnitude of LTP by increasing the density of silent synapses which express NMDARs containing NR2B subunits; AIM 2 will test the hypothesis that E2 mediated effects on spine density and synaptic function are not limited to the Schaffer collateral pathway but also include synapses between the entorhinal cortex and the distal dendrites of CA1 pyramidal cells; AIM3 will test the hypothesis that cholinergic denervation will prevent the E2 induced increase in spine density, NMDAR transmission, and LTP magnitude but that sympathetic sprouting from the superior cervical ganglia will rescue these deficits; AIM 4 will test the hypothesis that prolonged hormone loss combined with normal aging prevents the ability of E2 replacement to induce morphological and functional changes at CA3-CA1 synapses.