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

 描述(申请人提供)：肌萎缩侧索硬化症(ALS)总是一种致命的神经肌肉疾病，其基础是整个大脑和脊髓的运动神经元(MN)变性。MNS的兴奋性是一种重要的神经保护内源性机制，在疾病过程中早期调节兴奋性可以在ALS中重新启动神经保护机制。然而，在疾病进展过程中，症状前兴奋性是如何被调节的，目前还不完全清楚。我们的长期目标是描述MN兴奋性的潜在机制，并建立能够促进生存和保护功能的目标，从而延缓疾病的发生和进展。在这一应用中，我们试图研究选择性易感的脑干MN突触特性的早期差异性改变。 与相对抵抗退化的MN相比，ALS。这项拟议研究的一个关键组成部分是在ALS的SOD1G93A小鼠模型中比较疾病易损性三叉神经运动神经元(TMN)和难治性动眼神经(OMN)在发育早期(P8-P12)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分为快速疲劳、快速抗疲劳和慢速三种运动单位类型，以评估优先容易退化的快速疲劳运动单位的差异变化。在目前的研究中，我们将使用这种分类策略，并使用体外膜片钳电生理和分子方法来评估突触兴奋性的变化和潜在的离子基础。此外，我们将利用独特的脑干感觉运动回路，涉及脆弱的TMN和位置较近的感觉中脑V(MES V)神经元，这些神经元从颌骨更近的肌梭提供单突触本体感觉输入，并形成中枢神经系统中唯一的初级感觉细胞。通过比较接受MES V输入的JC三叉神经MN和缺乏纺锤体输入的JO三叉神经MN的突触特性变化，我们将能够对功能不同的运动池中的选择性突触易损性提出新的主张。在建议的工作范围内，我们将研究抑制甘氨酸和GABA能(目标1)和兴奋性谷氨酸(目标2)到JC和JO TMN以及OMN的突触电流，进一步区分这些结果之间的运动单位类型。最后，我们将开发一个颌骨伸展反射电路的动态模型和一个简化的中央模式生成器来驱动TMN的节奏活动，例如在有节奏的咀嚼过程中，以测试突触变化的功能结果(目标3)。最近，使用基于计算机的颌骨闭合运动池模型，我们展示了SOD1ALS小鼠三叉神经运动单位兴奋性改变的功能结果。在这里，除了观察到的突触变化之外，我们还将把这些内在的兴奋性变化结合在一起，为研究ALS疾病易损性和进展的新的基于电路的假说铺平道路。突触衰竭在其他神经退行性疾病中也很明显，包括阿尔茨海默氏症、亨廷顿氏症和帕金森氏症，因此，我们拟议的研究将为基本了解ALS的疾病发展提供新的研究方向。

 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.