A novel method for transient and repeatable axonal tracing in developing marmosets

项目摘要 神经发育障碍（NDD）的临床前动物模型，包括自闭症谱系障碍（ASD） 和智力残疾，已经深入了解候选遗传病因，但电路水平 行为改变（特别是社交障碍）的潜在假设仍然难以捉摸。一 开发生物标志物和诊断工具的重大挑战是技术上的，因为典型的 神经束追踪技术需要死后组织的组织学，回路的纵向评估， 发展很少，而且相距甚远。为了解决这一关键的未满足的需求，我们建议开发一种新的， 短暂的，可重复的方法，完全避免了侵入性组织化学，并允许纵向 发育中的绒猴的轴突水平追踪。普通的绒猴（Callithrix jacchus）是一种理想的 用于研究与异常社会发展相关的电路轨迹的临床前建模物种。我们最近 发现，和人类一样，绒猴的额叶皮层也有社会选择性的面孔处理补丁。 因此，绒猴可以概括灵长类特有的社会行为方面，形成诊断标准 对于许多NDD。在目标1中，我们将优化我们的方法，该方法使用经颅聚焦超声（FUS） 将MnCl 2（一种磁共振成像（MRI）可见的轴突示踪剂）输送到大脑的任何指定区域。 在目标2中，我们试图证明FUS-MEMRI技术是一种可靠的筛选工具， 电路级畸变与重测信度。我们将利用我们基因多样的繁殖群体 研究自然发生的社会面孔处理差异的结构基础， 从小就从两个月到成年，我们将采用FUS-MEMRI方法跟踪轴突 我们先前在内侧额叶皮层中发现的社会选择性面部斑块的连通性。这种循环是 表面上参与分配社会显着性的面孔，一个典型的标志性缺陷的自闭症。通过使用我们的 建立fMRI范式-这是被动的，可以用于非常年轻的绒猴-我们将连接轴突 在面孔的社会处理中的功能变异性。另外，我们会雇佣训练有素的机器- 学习算法以将凝视模式与相关面部特征隔离，提供面部行为指数 处理.通过这种无创多模式方法，我们将建立其健康变异性的参数 在我们的绒猴种群的电路，奠定了遗传和药理学模型，目前在 我们的实验室和其他人。这项工作将导致建立一个新的非侵入性 纵向轴突追踪的方法是短暂的，有针对性的，可重复的。这项技术将具有广泛的 在转化研究中的应用，特别是神经发育应用，提供了一种非 侵入性地跟踪神经病理学出现的电路功能障碍，从一个年轻的年龄。为纵向 技术，FUS-MEMRI方法也非常适合于跟踪旨在确定治疗效果的治疗结果。 NDD早期治疗策略的有效性。

PROJECT SUMMARY Preclinical animal models of neurodevelopmental disorders (NDDs), including autism spectrum disorders (ASDs) and those of intellectual disabilities, have yielded insight into candidate genetic etiologies, but circuit-level hypotheses underlying behavioral alterations (particularly social impairments) have remained elusive. A significant challenge for developing biomarkers and diagnostic tools has been technological – because canonical neuronal tract-tracing techniques require histology of post-mortem tissue, longitudinal assessments of circuit development are few and far between. To address this critical unmet need, we propose to develop a novel, transient, and repeatable method that circumvents invasive histochemistry altogether and allows for longitudinal axonal-level tracing in developing marmoset monkeys. The common marmoset (Callithrix jacchus) is an ideal preclinical modeling species for studying circuit trajectories related to aberrant social development. We recently discovered that marmosets, like humans, possess socially selective face processing patches in frontal cortex. As such, marmosets can recapitulate primate-specific aspects of social behaviors that form the diagnostic criteria for many NDDs. In Aim 1, we will optimize our approach, which uses transcranial focused ultrasound (FUS) to deliver MnCl2, a magnetic resonance imaging (MRI)-visible axonal tracer to any prescribed region of the brain. In Aim 2, we seek to demonstrate that the FUS-MEMRI technique is a reliable screening tool for developmental circuit-level aberrations with test-retest reliability. We will leverage our genetically diverse breeding colony of marmosets to study the structural underpinnings of naturally occurring differences in social face processing from an early age. From two months into adulthood, we will employ the FUS-MEMRI method to track the axonal connectivity of our previously identified socially selective face patch in medial frontal cortex. This circuity is ostensibly involved in assigning social salience to faces, a classic hallmark deficit in ASDs. By employing our established fMRI paradigm – which is passive and can be used with very young marmosets – we will link axonal development to functional variability in social processing of faces. Further, we will employ trained machine- learning algorithms to isolate gaze patterns to relevant facial features, providing a behavioral index of face processing. With this noninvasive multimodal approach, we will establish parameters of healthy variability of this circuitry in our marmoset population, laying the groundwork for genetic and pharmacological models currently in development by our laboratory and others. This work will lead to the establishment of a novel noninvasive approach for longitudinal axonal tracing that is transient, targeted, and repeatable. This technique will have broad application in translational research, especially for neurodevelopmental applications, providing a means to non- invasively track the neuropathological emergence of circuit dysfunction from a young age. As a longitudinal technique, the FUS-MEMRI method is also well suited to track therapeutic outcomes aimed at determining the efficacy of early treatment strategies for NDDs.