PROPERTIES OF NICOTINIC RECEPTORS IN MUTANT MICE

据估计，发达国家的烟草使用导致近20%的死亡，使其成为过早死亡的最大单一因素（Peto et al.，1992年）。尼古丁是烟草中支持持续使用的主要成分，可能通过最初作用于烟碱乙酰胆碱受体（nAChR）来发挥其行为效应。该项目研究nAChR在突触的基本特性，期望这些特性是其他两个项目中研究的一些系统生理学和行为的基础。该应用程序的重点是nAChRs如何响应吸烟者所经历的尼古丁浓度变化。随着尼古丁浓度的变化，nAChR的群体分布在功能状态（即激活、脱敏和长期失活状态）中，这些状态可能是尼古丁介导的奖赏的基础，并有助于耐受性和戒断。在定量确定nAChRs介导的钙信号后，我们将确定这些钙信号如何调节海马突触。最后，我们将确定nAChRs的活性变化如何调节腹侧被盖区神经元的反应。膜片钳电生理学，定量钙测量和荧光技术将被用来调查的假设，尼古丁提供吸烟激活和脱敏nAChR，这是不断分布在功能状态。微岛培养物和脑切片将用于研究突变小鼠的组织，这是本计划项目应用的基本和统一工具。这项工作最初将利用缺乏α 3，α 5，α 7或β 2的突变小鼠，以及含有α 7（L247T）亚基的小鼠，其表现出减弱的脱敏作用。所有这些小鼠目前都是可用的。由于吸烟者大脑中nAChR的数量增加，因此有人认为成瘾的吸烟者用尼古丁来控制nAChR脱敏和失活的水平。因此，我们对nAChRs功能状态变化的研究可能对理解尼古丁成瘾的根本问题具有直接重要性。

Tobacco use in developed countries has been estimated to cause nearly 20% of all deaths, making it the largest single contributor to premature death (Peto et al., 1992). Nicotine is the primary component of tobacco that supports continued use, presumably exerting its behavior effects by initially acting upon nicotinic acetylcholine receptors (nAChRs). This project investigates basic properties of nAChRs at synapses, with the expectation that those properties underlie some of the systems physiology and behaviors investigated in the other two projects. The application focuses on how nAChRs respond to the changing concentrations of nicotine experienced by a smoker. As the nicotine concentrations changes, the population of nAChRs distributes among functional states (i.e. activated, desensitized, and long-term inactivated states) that may underlie the reward mediated by nicotine as well as contributing to aspects of tolerance and withdrawal. After determining quantitatively the calcium signals mediated by nAChRs, we will determine how those calcium signals may modulate hippocampal synapses. Finally, we will determine how the changing activity of nAChRs modulates the responses of ventral tegmental area neurons. Patch clamp electrophysiology, quantitative calcium measurements, and fluorescence techniques will be used to investigate the hypothesis that nicotine delivered by smoking activates and desensitizes nAChRs, which are constantly distributing among functional states. Microisland cultures and brain slices will be used to study tissue from mutant mice, which serve as the fundamental and unifying tool for this Program Project application. The work will initially utilize mutant mice lacking alpha3, alpha5, alpha7, or beta2, and the mouse containing the alpha7 (L247T) subunit, which exhibits diminished desensitization. All of these mice are presently available. Because the number of nAChRs is increased in the brains of smokers, it has been argued that addicted smokers medicate themselves with nicotine to control the level nAChR desensitization and inactivation. Thus, our studies of the changing functional states of nAChRs may have direct importance for understanding issues fundamental to nicotine addiction.