AMPA- and GABA(A) receptor signalling and corticospinal motor neuron excitability in mouse models of ALS

我们身体的正常功能依赖于大脑神经细胞之间以及神经细胞与周围组织之间的化学通讯。向肌肉传递信息的神经细胞被称为运动神经元。这些神经元的进行性和选择性死亡是使人衰弱并最终致命的神经退行性疾病肌萎缩性侧索硬化症（ALS）的一个典型特征。如果没有正确的输入，肌肉就无法发挥作用，肌肉会变弱和浪费，使患者无法自主运动。在被认为导致运动神经元丧失的机制中，由细胞内钙离子升高引发的“兴奋毒性损伤”被认为是特别重要的。像其他神经细胞一样，运动神经元接受由神经递质谷氨酸介导的兴奋性信号，谷氨酸通过与细胞之间接触点的受体蛋白结合而起作用。钙缓冲能力差和一种允许钙离子进入的ampa型谷氨酸受体亚类的表达被认为是ALS运动神经元易损的原因。然而，运动神经元中钙透性AMPA受体功能和调控的细节尚不清楚。转基因啮齿动物提供了有价值的疾病模型，但是使用膜片钳记录（一种允许对细胞电活动进行高分辨率检查的技术）研究脊髓运动神经元只能在未成熟、无症状的动物中进行。与脊髓中的运动神经元不同，皮层中的“上部”运动神经元（也会在ALS中发生退化）可以在成熟动物的切片中进行膜片钳记录。我们计划利用这一点，选择性地标记这些皮质脊髓运动神经元（csmn），使我们能够记录ALS小鼠急性脑切片中处于不同疾病进展阶段的已识别运动神经元。我们希望研究csmn中钙渗透性AMPA受体的普遍性和调控，并确定由不同的神经递质受体GABA(a)受体介导的抑制性输入的变化如何促进ALS中运动神经元的兴奋性，从而导致兴奋性毒性损伤。通过对对照动物和有症状动物的运动神经元进行电生理研究，该项目将揭示正常脑功能，并为肌萎缩侧索硬化症中运动神经元易损机制的悬而未决的问题提供答案。

The proper function of our bodies relies on the chemical communication that takes place among nerve cells in the brain and between nerve cells and peripheral tissues. Nerve cells that convey information to muscles are known as motor neurons. The progressive and selective death of these neurons is a defining feature of the debilitating, and ultimately fatal, neurodegenerative disease Amyotrophic Lateral Sclerosis (ALS). Unable to function without correct input, the muscles weaken and waste, leaving the patient incapable of voluntary movement. Among the mechanisms thought contribute to this motor neuron loss, 'excitotoxic damage' triggered by elevation of intracellular calcium ions is held to be especially important. Like other nerve cells, motor neurons receive excitatory signals mediated by the neurotransmitter glutamate, which acts by binding to receptor proteins at points of contact between the cells. A combination of poor calcium buffering capacity and the expression of one subclass of AMPA-type glutamate receptors that allow the entry of calcium ions, is thought to contribute to the vulnerability of motor neurons in ALS. However, details of calcium-permeable AMPA receptor function and regulation in motor neurons are poorly understood. Transgenic rodents provide valuable models of the disease, but the study of spinal motor neurons using patch-clamp recording (a technique allowing high-resolution examination of a cell's electrical activity) is possible only in immature, asymptomatic, animals. Unlike motor neurons in the spinal cord, 'upper' motor neurons in the cortex, which also undergo degeneration in ALS, are amenable to patch-clamp recording in slices from mature animals. We plan to take advantage of this, and selectively label these corticospinal motor neurons (CSMNs), allowing us to record from identified motor neurons in acute brain slices from 'ALS' mice at different stages of disease progression. We wish to examine the prevalence and regulation of calcium-permeable AMPA receptors in CSMNs and determine how changes in inhibitory input mediated by a different neurotransmitter receptor, the GABA(A) receptor, contribute to motor neuron excitability, and thus excitotoxic damage, in ALS. By performing electrophysiological studies of motor neurons in both control and symptomatic animals, this project will shed light on normal brain function and provide answers to outstanding questions regarding the mechanisms underlying vulnerability of motor neurons in ALS.