Cholinergic signaling in cortical neurons: a unifying hypothesis

描述(申请人提供)：乙酰胆碱(ACh)在认知中起关键作用，大脑皮层胆碱能输入减少导致阿尔茨海默病、路易体痴呆、帕金森痴呆和其他神经系统疾病的认知缺陷。然而，缺乏关于胆碱能效应的药理学知识，或者ACh影响神经元活动的机制，阻碍了针对这些衰弱疾病的特异性治疗的发展。确实存在的数据似乎相互冲突，而且很难协调。事实上，ACh矛盾地在提供大部分皮质输出的深层锥体神经元中产生两种相反的反应：快速的瞬时抑制和更持久的兴奋。虽然在这些神经元中介导抑制性胆碱能反应的机制(M1样乙酰胆碱受体激活、细胞内钙库钙释放，以及随后激活SK型钙激活的钾电导)已被很好地描述，但介导胆碱能兴奋的机制以及兴奋性和抑制性胆碱能信号之间的功能关系仍不清楚。该项目旨在确定皮质第5层锥体神经元胆碱能兴奋的受体亚型、信号级联和离子机制，并测试ACh的兴奋作用反映了钙渗透的非选择性阳离子电导的激活，该阳离子电导起到补充细胞内钙储存的功能，从而阻断抑制胆碱能信号的作用。我们建议在脑片制备中使用电生理和成像方法来解决以下三个特定目的：1.确定在新皮质第五层锥体神经元中介导胆碱能兴奋和抑制的特异性M受体(S)。2.探讨5层神经元胆碱能兴奋的信号转导和离子机制。3.检验兴奋性胆碱能传导对抑制胆碱能信号转导过程中耗尽的细胞内钙离子的补充作用这一统一假设。我们的结果将为理解胆碱能促进认知功能的生物学基础提供一个框架。这一新知识将增加我们对为什么胆碱能系统功能障碍导致痴呆和其他疾病状态下观察到的功能缺陷的理解，并将为治疗干预提供新的靶点。与公共卫生相关：乙酰胆碱是一种正常认知功能所必需的大脑化学物质，乙酰胆碱的丧失与阿尔茨海默病和其他疾病状态有关。该项目将确定乙酰胆碱影响正常大脑皮层神经元活动的生物学机制，目的是了解为什么乙酰胆碱在衰老或疾病期间丢失会导致认知功能障碍。

DESCRIPTION (provided by applicant): Acetylcholine (ACh) plays a critical role in cognition, and decreased cholinergic input to the cerebral cortex contributes to the cognitive deficits observed in Alzheimer's disease, dementia with Lewy Bodies, Parkinson's dementia, and other neurological diseases. However, a lack of knowledge regarding the pharmacology of cholinergic effects, or the mechanisms by which ACh influences neuronal activity, have hampered the development of therapies specific to these debilitating diseases. The data that do exist appear conflicting, and have been difficult to reconcile. Indeed, ACh paradoxically generates two opposing responses in the deep-layer pyramidal neurons that provide the majority of cortical output: a fast transient inhibition and a longer-lasting excitation. Although the mechanisms mediating inhibitory cholinergic responses in these neurons (M1-like muscarinic acetylcholine receptor activation, calcium- release from intracellular calcium stores, and subsequent activation of an SK-type calcium-activated potassium conductance) have been well described, the mechanisms mediating cholinergic excitation, and the functional relationship between excitatory and inhibitory cholinergic signaling, remain unknown. This project aims to determine the receptor subtypes, signaling cascades, and ionic mechanisms responsible for cholinergic excitation in cortical layer 5 pyramidal neurons, and to test the overarching hypothesis that excitatory actions of ACh reflect activation of a calcium-permeable non-selective cationic conductance that acts functionally to replenish the intracellular calcium stores that gate inhibitory cholinergic signaling. We propose to use electrophysiological and imaging approaches in a brain slice preparation to address the following three specific aims: 1. To identify the specific muscarinic receptor(s) mediating cholinergic excitation and inhibition in neocortical layer 5 pyramidal neurons. 2. To determine the signaling cascades and ionic mechanism responsible for cholinergic excitation of layer 5 neurons. 3. To test the unifying hypothesis that excitatory cholinergic conductances serve functionally to refill intracellular calcium stores depleted during inhibitory cholinergic signaling. Our results will provide a framework for understanding the biological basis for cholinergic facilitation of cognitive function. This new knowledge will increase our understanding of why dysfunction of cholinergic systems leads to the functional deficits observed in dementia and other disease states, and will provide new targets for therapeutic intervention. The Public Health Relevance: Acetylcholine is a brain chemical necessary for normal cognitive function, and loss of acetylcholine is associated with Alzheimer's disease and other disease states. This project will determine the biological mechanisms by which acetylcholine influences the activity of neurons in the normal cerebral cortex, with the aim of understanding why loss of acetylcholine during aging or disease leads to cognitive dysfunction.