Modeling Synaptic Vulnerability of a Brainstem Sensorimotor Circuit in a Mouse Model for Amyotrophic Lateral Sclerosis

 描述（由申请人提供）：肌萎缩性侧索硬化症（ALS）是一种致命的神经肌肉疾病，是整个大脑和脊髓运动神经元（MN）变性的基础。MN的兴奋性是神经保护的重要内源性机制，并且在疾病过程的早期调节兴奋性可以在ALS中招募神经保护机制。然而，还没有完全理解症状前兴奋性在疾病进展过程中是如何调节的。我们的长期目标是阐明MN兴奋性的潜在机制，并建立可以促进生存和保护功能的靶点，从而延迟疾病的发作和进展。在本申请中，我们试图研究选择性地易受以下因素影响的脑干MN的突触特性的早期差异改变： ALS与相对抗变性的MN相比。拟议研究的一个关键组成部分是比较疾病脆弱的三叉神经运动神经元（TMN）与抗性眼神经元（OMN）在发育早期（P8-P12）在充分表征的SOD 1G 93 A小鼠模型ALS的突触兴奋性变化。我们将进一步利用我们最近提出的聚类方法将MN分类为各自的运动单位类型，如快速疲劳，快速抗疲劳和缓慢，以评估快速疲劳运动单位的差异性改变，这些运动单位优先容易退化。在本研究中，我们将利用这种分类策略，并评估突触兴奋性的变化和潜在的离子基础，使用体外膜片钳电生理和分子方法。此外，我们将利用一个独特的脑干感觉运动回路，涉及脆弱的TMN和位置紧密的感觉中脑V（Mes V）神经元，提供单突触本体感受输入从下颌近肌梭，并形成中枢神经系统内唯一的初级感觉细胞。通过比较突触特性的下颌闭合器（JC）三叉神经MN，接受Mes V输入与确定的下颌开口器（JO）三叉神经MN，缺乏纺锤体输入的变化，我们将能够在功能不同的运动池内的选择性突触脆弱性提出新的要求。在拟议的工作范围内，我们将研究抑制性甘氨酸和GABA能（目标1）和兴奋性谷氨酸能（目标2）突触电流JC和JO TMN以及OMN，进一步区分这些结果之间的运动单位类型。最后，我们将开发一个动态模型的下颌牵张反射电路和一个简化的中央模式发生器驱动TMN的节奏活动，如在节奏咀嚼测试突触改变的功能结果（目的3）。最近，使用计算机为基础的模型的下巴关闭电机池，我们证明了功能的结果，在三叉神经运动单位兴奋性的改变，在SOD 1 ALS小鼠。在这里，我们将把这些内在的兴奋性变化，除了观察到的突触变化一起铺平道路，为ALS疾病的脆弱性和进展的一种新的基于电路的假说。突触失效在其他神经退行性疾病中是明显的，包括阿尔茨海默氏症、亨廷顿氏症和帕金森氏症，因此，我们提出的研究将在ALS疾病发展的基本理解中提供新的研究方向方面至关重要。

 DESCRIPTION (provided by applicant): Amyotrophic Lateral Sclerosis (ALS) is an invariably fatal neuromuscular disease underlying degeneration of motoneurons (MN) throughout the brain and spinal cord. Excitability of MNs is a crucial endogenous mechanism of neuroprotection and modulating excitability early in the disease process can recruit neuroprotective mechanisms in ALS. However, it is not fully understood how pre- symptomatic excitability is modulated during disease progression. Our long-term goals are to delineate mechanisms underlying MN excitability and establish targets that can promote survival and preserve function resulting in delayed disease onset and progression. In this application, we seek to investigate early differential alterations in synaptic properties of brainstem MNs that are selectively vulnerable to ALS in comparison to MNs that are relatively resistant to degeneration. A key component of the proposed study is to compare synaptic excitability changes in disease vulnerable trigeminal motor neurons (TMNs) versus resistant oculomotor neurons (OMNs) at an early developmental stage (P8-P12) in the well-characterized SOD1G93A mouse model for ALS. We will further capitalize on our recently proposed clustering approach to classify MNs into their respective motor unit types as fast fatigable, fast fatigue resistant and slow, to assess differential alterations in fast fatigable motor units that are preferentially vulnerable to degeneration. In th current study, we will utilize this classification strategy and assess changes in synaptic excitability and the underlying ionic basis using in vitro patch-clamp electrophysiological and molecular approaches. Additionally, we will leverage a unique brainstem sensorimotor circuit involving vulnerable TMNs and the closely located sensory mesencephalic V (Mes V) neurons that provide monosynaptic proprioceptive inputs from jaw closer muscle spindles and form the only primary sensory cells within the central nervous system. By comparing alterations in synaptic properties of jaw closer (JC) trigeminal MNs that receive Mes V inputs with identified jaw opener (JO) trigeminal MNs that lack spindle inputs, we will be able to make novel claims on selective synaptic vulnerability within functionally distinct motor pools. Within the scope of proposed work, we will examine inhibitory glycine and GABAergic (Aim 1) and excitatory glutamatergic (Aim 2) synaptic currents to JC and JO TMNs as well as to OMNs, further distinguishing these results between motor unit types. Finally, we will develop a dynamic model of jaw stretch reflex circuit and a simplified central pattern generator driving rhythmic activity n TMNs such as during rhythmic chewing to test the functional outcome of synaptic alterations (Aim 3). Recently, using a computer-based model of the jaw closer motor pool, we demonstrated a functional outcome of the alterations in trigeminal motor unit excitability in the SOD1 ALS mouse. Here we will incorporate those intrinsic excitability changes in addition to the observed synaptic changes together paving the way for a novel circuitry-based hypothesis for disease vulnerability and progression in ALS. Synaptic failure is evident in other neurodegenerative diseases including Alzheimer's, Huntington's and Parkinson's, and, therefore our proposed studies will be crucial in providing novel research directions in the basic understanding of disease development in ALS.