Nicotinic Control of Non-Nicotinic Synapses in the Hippocampus

描述（由申请人提供）：在哺乳动物中，烟碱胆碱能信号通过递质乙酰胆碱激活具有阳离子选择性的配体门控离子通道。这种形式的信号在神经系统中广泛存在，在出生后早期达到峰值，并持续到成年期。它有助于包括觉醒和认知在内的各种行为，参与许多神经退行性疾病，包括阿尔茨海默病和帕金森病，并负责尼古丁成瘾。尽管付出了巨大的努力，但人们对尼古丁信号在发育过程中驱动神经系统自发兴奋波的作用知之甚少，对尼古丁随后在成人大脑网络中发挥全球作用的机制也知之甚少。这一提议测试了两个对这些问题至关重要的新假设。首先，发育过程中的尼古丁信号传导促进了出生后早期和成年神经元上谷氨酸能突触的形成（Aims I & II）。由于谷氨酸能通路提供大脑兴奋的主要形式，这种尼古丁输入的影响可能对神经系统功能产生持久的影响。第二种假设是，成人大脑中的尼古丁活动可以剧烈且可逆地改变gaba能信号，使其停止抑制性并短暂地变得兴奋（Aim III）。这可能对整个网络产生深远影响，从根本上改变产出。对海马体的初步研究有力地支持了这些观点。两种主要的烟碱乙酰胆碱受体，同戊二胺？7- nachr和异戊美？2-含nachr，似乎在促进谷氨酸突触形成方面相互补充。其中一个似乎以细胞自主的方式驱动突触后棘的形成，而另一个可能间接地招募突触功能所需的成分。初步结果也支持第二种假设：烟草使用者所经历的低水平尼古丁可能足以暂时逆转成年神经元中的氯梯度，从而使GABA暂时去极化。这可能会极大地改变容纳这些神经元的网络的兴奋性。这些假设将通过药理学和基因操作进行测试，包括在海马切片和体内进行功能丧失和拯救实验。将分析潜在的分子机制，并评估其对系统功能的影响。成像和电生理方法将结合在这个分析中。这里提出的实验测试了神经系统中尼古丁胆碱能信号传导的关键思想。这一结果可能会改变我们对指导神经网络发展和功能调节的基本过程的看法。这些过程易受烟草衍生尼古丁利用的脆弱性使这项工作具有引人注目的健康相关意义。公共卫生相关性：该项目将测试内源性尼古丁胆碱能信号在塑造发育中的神经系统和随后在成人中控制功能中的作用的新想法。由于这些途径与烟草消费中尼古丁劫持的途径相同，因此这些研究还将提供有关处于危险中的系统和可能随之而来的后果的重要信息。除了解决神经系统功能的基本问题外，这些研究还可以确定治疗干预的目标，以逆转或纠正生物缺陷，并减轻习惯性烟草使用的影响。

DESCRIPTION (provided by applicant): Nicotinic cholinergic signaling uses the transmitter acetylcholine to activate ligand-gated ion channels that are cation-selective in mammals. This form of signaling is widespread in the nervous system, reaches peak levels during early postnatal life, and continues throughout adulthood. It contributes to a variety of behaviors including arousal and cognition, participates in a number of neurodegenerative disorders including Alzheimer's and Parkinson's diseases, and is responsible for nicotine addiction. Despite intensive effort, little is understood about the role of nicotinic signaling during development when it drives spontaneous waves of excitation across the nervous system, and little is understood about the nicotinic mechanisms that subsequently exert global effects across networks in the adult brain. This proposal tests two novel hypotheses fundamental to these issues. The first is that nicotinic signaling during development promotes the formation of glutamatergic synapses both on early postnatal and adult born neurons (Aims I & II). Since glutamatergic pathways provide the principal form of excitation in brain, this effect of nicotinic input is likely to have lasting consequences for nervous system function. The second hypothesis is that nicotinic activity in the adult brain can acutely and reversibly alter GABAergic signaling such that it stops being inhibitory and transiently becomes excitatory (Aim III). This could exert far-reaching effects across networks radically altering output. Preliminary studies performed on the hippocampus strongly support these ideas. The two major nicotinic acetylcholine receptors, homopentameric ?7-nAChRs and heteropentameric ?2-containing nAChRs, appear to complement each other in promoting glutamate synapse formation. One appears to act in cell-autonomous fashion to drive postsynaptic spine formation while the other may act indirectly to recruit components required for synaptic function. Preliminary results also support the second hypothesis: low levels of nicotine experienced by tobacco users may be sufficient to transiently invert the chloride gradient in adult neurons, thereby rendering GABA temporarily depolarizing. This could dramatically change the excitability of networks housing those neurons. The hypotheses will be tested by pharmacological and genetic manipulation, including loss-of-function and rescue experiments, performed on hippocampal slices and in vivo. The underlying molecular mechanisms will be analyzed and their consequences evaluated for system function. Imaging and electrophysiological approaches will be combined in this analysis. The experiments proposed here test pivotal ideas about the purpose of nicotinic cholinergic signaling in the nervous system. The results are likely to change how we think about fundamental processes guiding development and regulation of function in neural networks. The vulnerability of these processes to exploitation by tobacco-derived nicotine gives this work compelling health-related significance. PUBLIC HEALTH RELEVANCE: This project will test new ideas about the roles of endogenous nicotinic cholinergic signaling in shaping the developing nervous system and controlling function subsequently in the adult. Because these are the same pathways hijacked by nicotine from tobacco consumption, the studies will also provide important information about the systems at risk and consequences likely to ensue. In addition to addressing fundamental aspects of nervous system function, the studies may identify targets for therapeutic intervention both to reverse or to correct biological deficiencies and to mitigate the impact of habitual tobacco use.