Direct nicotinic excitation of layer 5 neocortical pyramidal neurons

描述（由申请人提供）：新皮层在许多高阶功能中起着核心作用，如解释感觉信息，理解语言和控制自主运动。许多这些过程是由基底前脑复合体（主要是基底核）神经元的上升胆碱能驱动形成的。这条通路的功能障碍导致许多涉及新皮层的行为缺陷，并与抑郁症、帕金森病和阿尔茨海默病等临床疾病有关。我们的长期目标是了解基底核乙酰胆碱如此深刻地影响皮质功能的细胞和网络机制。乙酰胆碱和烟碱乙酰胆碱受体（machr和nachr）作用于乙酰胆碱和烟碱乙酰胆碱受体，这两种受体在大脑皮层广泛表达。新皮层锥体神经元表达这两种受体，但锥体神经元中nachr的生理功能尚不清楚。在这个提议中，我们描述了nachr在锥体神经元上的功能。我们利用光遗传学、病毒工具、转基因小鼠、免疫细胞化学、细胞电生理学、双光子显微镜和电子显微镜等综合技术，直接评估基底核轴突释放的乙酰胆碱如何影响运动皮层的锥体神经元。我们在基底核的胆碱能神经元及其新皮层轴突中表达通道视紫红质-2。在初步实验中，胆碱能轴突的激活去极化并通过nachr促进第5层锥体神经元的尖峰，这使我们假设ACh促进了信息通过新皮质网络从上升的兴奋输入（如丘脑）到目标结构（如脊髓的运动回路）的传递。在这个

DESCRIPTION (provided by applicant): The neocortex plays a central role in many higher-order functions such as the interpretation of sensory information, comprehension of language and control of voluntary movements. Many of these processes are shaped by ascending cholinergic drive from neurons in the basal forebrain complex, principally nucleus basalis. Dysfunction of this pathway leads to deficits in many behaviors that involve neocortex and has been tied to clinical conditions such as depression, Parkinson's disease and Alzheimer's disease. Our long-term aim is to understand the cellular and network mechanisms by which ACh from nucleus basalis so profoundly influences cortical function. ACh acts at muscarinic and nicotinic ACh receptors (mAChRs and nAChRs), which are widely expressed in neocortex. Pyramidal neurons in neocortex express both of these receptor types, but the physiological functions of nAChRs in pyramidal neurons are unknown. In this proposal we describe the functions of nAChRs on pyramidal neurons. We directly assess how ACh, released by axons from nucleus basalis, affects pyramidal neurons in motor cortex, using a combination of techniques, including optogenetics, viral tools, genetically-modified mice, immuno-cytochemistry, cellular electrophysiology, two-photon microscopy and electron microscopy. We express channelrhodopsin-2 in cholinergic neurons in nucleus basalis and their axons in neocortex. In preliminary experiments, activation of cholinergic axons depolarized and promoted spiking of layer 5 pyramidal neurons via nAChRs, leading us to hypothesize that ACh facilitates the transfer of information through neocortical networks from ascending excitatory inputs, e.g. from thalamus, to target structures, e.g. motor circuits in the spinal cord. In this proposal we will determine whether the effects of ACh on pyramidal neurons support this hypothesis. We will investigate the mechanisms by which nAChRs affect spiking and the nAChR receptor subunits involved (specific aim 1), determine where in the activated nAChRs are located within the dendritic trees of pyramidal neurons (specific aim 2), and determine whether these postsynaptic nAChRs mediated the effects of ACh in pyramidal neurons in other layers and neocortical areas (specific aim3). Our results will reveal a new mechanism by which ACh modulates the excitability of pyramidal neurons. Our studies will also provide the first evidence, to my knowledge, that ACh has layer-specific effects. The resulting hypothesis has the potential to transform our understanding of the manner in which the cholinergic pathway from nucleus basalis changes network function in neocortex and may therefore have important implications for debilitating conditions such as Parkinson's disease and Alzheimer's disease.