Neural basis of locomotor dysfunction in Down Syndrome

项目总结 唐氏综合征(DS)是最常见的染色体疾病，也是最常见的遗传疾病 美国智力残疾的原因。DS影响儿童的一系列行为领域，包括运动 和认知功能。虽然非典型认知加工在DS、运动功能障碍方面已经得到了很好的研究 对此研究相对较少。临床评估表明，DS患者存在一系列运动障碍，甚至速度较慢 自适应控制。纵向数据还表明，从童年到成年，步态发生了变化。小脑 病理学在DS中一直被观察到，并被认为与运动和运动功能障碍有关 自适应运动技能。对DS动物模型的研究也表明，小脑处理能力不足。 然而，潜伏在运动障碍和小脑回路中的特定通路在 DS仍然知之甚少。定义运动行为的特定异常，并识别大脑 功能相关的区域和神经元将为开发潜在的治疗方法提供基础 治疗DS患者的运动问题。这项提案的主要目标是确定具体的变更 导致DS患者运动功能障碍的小脑回路。我们的初步数据显示 Ts65Dn的运动协调不良、适应性运动学习缺陷和小脑突触改变 DS小鼠模型。为了量化运动行为，我们使用了ErasmusLader，这是一种先进的工具，具有 测量运动协调性和自适应小脑学习。我们对出生后Ts65Dn小鼠的分析 结果显示，作为小脑皮质唯一输出的浦肯野细胞(PC)受到的兴奋性较少 攀升纤维突触(CFs)高于正常。这一发现意义重大，因为依赖小脑的学习 依赖于CFS对PC树突的强单突触兴奋性输入。根据我们的数据，我们 假设Ts65Dn小鼠DS模型中的运动功能障碍和适应性运动缺陷是 由PC的CF输入中断引起。为了验证这一假设，在目标1中，我们将定义PC电路的变化 这与PC的异常突触输入和Ts65Dn小鼠的运动学习缺陷有关。我们会 分析运动功能障碍并确定小脑回路的分子变化以确定潜在的突触 小脑皮层的改变。在目标2中，我们将建立 自由行为动物的PC活性和运动异常的病理生理变化，以及 确定增强对PC的兴奋性输入是否会恢复Ts65Dn小鼠的运动功能。我们会 使用我们实验室建立的先进技术，使用GCaMP6f光纤光度法来计时- 锁定PC在小脑中的活动，以擦除爬行行为数据。我们将尝试拯救异常情况 在Ts65Dn小鼠PC活动和运动行为中表达兴奋性DREADDS Ts65Dn小鼠下橄榄(IO；CFS的唯一来源)，然后选择性地注射氯氮平N-氧化物(CNO) 激活IO，通过CFS向PC提供持续和增强的兴奋性输入。

PROJECT SUMMARY Down syndrome (DS) is the most commonly diagnosed chromosomal condition and the most common genetic cause of intellectual disability in the US. DS affects a range of behavioral domains in children, including motor and cognitive function. While atypical cognitive processing has been well studied in DS, locomotor dysfunction is relatively understudied. Clinical assessments indicate a range of locomotor deficits in DS, as well as slower adaptive control. Longitudinal data also indicates altered gait evolution from childhood to adulthood. Cerebellar pathology has been consistently observed in DS, and is thought to contribute to dysfunction in locomotor and adaptive motor skills. Studies in animal models of DS have also indicated deficient cerebellar processing. However, the specific pathways underlying locomotor deficits and the cerebellar circuits that are disrupted in DS remain poorly understood. Defining specific abnormalities in motor behavior, and identifying the brain regions and neurons which are functionally involved will provide the basis for developing potential therapies for treating motor problems in individuals with DS. The main goal of this proposal is to identify specific alterations in the circuitry of the cerebellum that result in locomotor dysfunction in DS. Our preliminary data show locomotor miscoordination, adaptive motor learning deficits, and cerebellar synaptic alterations in the Ts65Dn mouse model of DS. To quantify locomotor behavior, we used the ErasmusLadder, an advanced tool capable of measuring locomotor coordination and adaptive cerebellar learning. Our analysis in postnatal Ts65Dn mice shows that Purkinje cells (PCs), which are the sole output of the cerebellar cortex, receive fewer excitatory synapses from climbing fibers (CFs) than normal. This finding is significant, as cerebellar-dependent learning depends on strong monosynaptic excitatory input from CFs onto PC dendrites. Based on our data, we hypothesize that locomotor dysfunction and adaptive motor deficits in the Ts65Dn mouse model of DS are caused by disruption of CF input to PCs. To test this hypothesis, in Aim 1 we will define changes in PC circuitry that are linked to abnormal synaptic input to PCs and to locomotor learning deficits in Ts65Dn mice. We will analyze locomotor dysfunction and identify molecular changes in cerebellar circuitry to define potential synaptic alterations in the cerebellar cortex. In Aim 2, we will establish the precise correlation between pathophysiological changes in PC activity and locomotor abnormalities in freely-behaving animals, and determine whether enhancing excitatory input to PCs will restore locomotor function in Ts65Dn mice. We will use an advanced technique established in our lab that employs GCaMP6f fiber photometry in order to time- lock PC activity in the cerebellum to ErasmusLadder behavioral data. We will attempt at rescuing abnormalities in PC activity and locomotor behavior in Ts65Dn mice by specifically expressing excitatory DREADDs in the inferior olive (IO; the sole origin of CFs) of Ts65Dn mice and then inject clozapine N-oxide (CNO) to selectively activate the IO, causing sustained and enhanced excitatory input to PCs via CFs.