Mechanisms of pathology and neuronal hyperactivity in a memory circuit in Alzheimer's disease

Tsai实验室先前的工作（Canter et al 2019）将乳头体（MB）确定为 在5XFAD模型小鼠中淀粉样蛋白沉积的第一个位点，也与 痴呆症的严重程度。小鼠MB的单细胞RNA测序鉴定出2 MB内不同的神经元群体，具有隔离分布、靶向投射和 独特的电生理学对5XFAD小鼠中这些群体的分析发现， 这些人群，即在外侧MB（LM）中发现的人群，是唯一易患多动症的人群 和神经变性，而第二群体（内侧MB，MM）在很大程度上不受影响。 LM群体的活动也直接有助于小鼠的记忆表现 任务此外，使用Boyden实验室的迭代直接扩展显微镜（idExM），我们 已经确定了与穹窿中特定投射相关的淀粉样蛋白的有趣模式， 来自下托的白色物质束具有到MB的轴突输入。该补助金旨在 研究MB和穹窿中淀粉样蛋白和兴奋性变化之间的联系，包括 开发实现这一目标所需的工具。在这个实验中要检验的假设 淀粉样蛋白优先与下托-LM投射相关， 这些轴突表现出过度兴奋性。Aim 1将绘制这个新的 LM神经元群体及其来自海马的上游输入，使用新的 开发了原位测序技术，以及探索白色物质中的病理学 该电路在5XFAD小鼠和人脑样本中的投射区域，最近使用 发展了扩张显微镜。目标2将描述 通过高级电压成像在LM神经元中发现的过度活跃，以及扩展这一点， 对其他AD小鼠模型的作用。目标3将利用光遗传学和药理学 确定特定异常回路活动是否驱动病理和行为的方法 在AD模型小鼠中观察到的变化。

Previous work from the Tsai lab (Canter et al 2019) identified the mamillary body (MB) as one of the first sites of amyloid deposition in 5XFAD model mice, a region that also correlates with dementia severity in human patients. Single cell RNA sequencing of the mouse MB identified 2 distinct neuronal populations within the MB, with segregated distribution, target projection, and unique electrophysiology. Analysis of these populations in the 5XFAD mice found that one of these populations, those found in the lateral MB (LM), are uniquely susceptible to hyperactivity and neurodegeneration, while the second population (medial MB, MM) is largely unaffected. The activity of the LM population also directly contributes to mouse performance in memory tasks. Additionally, using iterative direct-expansion microscopy (idExM) from the Boyden lab, we have identified intriguing patterns of amyloid associated with specific projections in the fornix, the white matter tract from the subiculum with axonal inputs to the MB. This grant proposes to investigate the links between amyloid and excitability changes in the MB and fornix, including development of the tools necessary to achieve this goal. The hypothesis to be tested in this application is that amyloid preferentially associates with the subiculum-LM projection and that these axons exhibit hyperexcitability. Aim 1 will map the connections between this new population of LM neurons and its upstream inputs from the hippocampus, using a newly developed in situ sequencing techniques, as well as exploring pathology in the white matter projection regions of this circuit in 5XFAD mice and human brain samples, using recently developed expansion microscopy. Aim 2 will characterize the source and location of hyperactivity found in the LM neurons through advanced voltage imaging, as well as expand this work to other mouse models of AD. Aim 3 will use optogenetics and pharmacological approaches to determine if specific aberrant circuit activity drives the pathology and behavioral changes seen in the AD model mice.