Imaging dendritic spine abnormalities and circuit defects in fragile X mice.

描述（由申请人提供）：脆性X综合征（FXS）是最常见的智力缺陷遗传形式，也是自闭症最常见的单基因原因。对Fmr1基因敲除（KO）小鼠（FXS的动物模型）的研究发现，大脑中存在两个主要缺陷。第一种是皮层兴奋性突触的主要受体树突棘的结构异常，第二种是突触和经验依赖性可塑性的功能异常。利用体内双光子显微镜，我们等人发现Fmr1 KO小鼠皮质锥体神经元树突棘的稳定和成熟发育迟缓，这可能是FXS最早的突触缺陷之一。现在，我们将验证由感觉体验触发的电路重塑与脊柱动力学和大小密切相关的假设，从而协调Fmr1 KO小鼠的结构和功能表型。我们还将利用电子显微镜在超微结构水平上研究突触的完整性，以及皮层发育过程中轴突及其钮扣的动力学，以确定它们是否在突变小鼠中也发生了改变。此外，利用体内双光子钙成像和电生理学记录完整电路中的神经元活动，我们发现Fmr1 KO小鼠的锥体神经元表现出异常高的放电率和同步性，这可以解释这些小鼠的学习缺陷和低癫痫阈值。在这里，我们将验证这种网络高兴奋性转化为感觉诱发活动问题的假设，我们将研究是否可以通过影响脑干神经调节和抑制通路的药物来挽救KO小鼠的这些回路水平问题。实验设计采用尖端的体内成像技术，旨在解决FXS中的重要知识空白和有争议的问题。由于树突状脊柱异常和许多由脆性X智力发育迟缓蛋白调节的信号通路也与其他神经发育障碍有关，我们相信我们独特的突触到电路方法具有非常高的意义，并且可能对许多类型的自闭症和精神障碍具有广泛的重要性。

DESCRIPTION (provided by applicant): Fragile X syndrome (FXS) is the most common inherited form of intellectual impairment and the most common single gene cause of autism. Research in Fmr1 knockout (KO) mice, an animal model of FXS, has identified two major defects in the brain. The first is a structural abnormality in dendritic spines, the major recipiens of excitatory synapses in the cortex, and the second is a functional abnormality in synaptic and experience- dependent plasticity. Using in vivo two-photon microscopy, we and others have identified a developmental delay in the stabilization and maturation of dendritic spines of cortica pyramidal neurons in Fmr1 KO mice, which may be one of the earliest synaptic defects in FXS. Now, we will test the hypothesis that circuit remodeling triggered by sensory experience is intimately tied to the spine dynamics and size, thereby reconciling the structural and functional phenotypes of Fmr1 KO mice. We will also investigate synapse integrity at the ultrastructural level with electron microscopy, as well as the dynamics of axons and their boutons during cortical development, in order to ascertain whether they are also altered in mutant mice. In addition, using in vivo two-photon calcium imaging and electrophysiology to record neuronal activity in intact circuits, we have shown that pyramidal neurons in Fmr1 KO mice show abnormally high firing rates and synchrony, which could explain the deficits in learning and low seizure threshold in these mice. Here, we will test the hypothesis that this network hyperexcitability translates into problems with sensory-evoked activity and we will investigate whether these circuit-level problems in KO mice can be rescued with drugs that affect brainstem neuromodulation and inhibitory pathways. The experimental design employs cutting edge in vivo imaging techniques and seeks to address important knowledge gaps and controversial issues in FXS. Because dendritic spine abnormalities and many of the signaling pathways regulated by the fragile X mental retardation protein are also implicated in other neurodevelopmental disorders, we believe that our unique synapse-to- circuit approach has a very high significance and is likely to be of broad importance to many types of autism and mental impairment.