PROPERTIES OF NICOTINIC RECEPTORS IN MUTANT MICE

发达国家的烟草使用估计占所有死亡人数的近20%，使其成为导致过早死亡的最大单一因素(Peto等人，1992年)。尼古丁是烟草中支持持续使用的主要成分，据推测，尼古丁最初通过作用于烟碱型乙酰胆碱受体(NAChRs)而对行为产生影响。这个项目研究了nAChRs在突触上的基本性质，期望这些性质是其他两个项目中研究的一些系统生理和行为的基础。该应用程序重点研究nAChRs如何对吸烟者经历的尼古丁浓度变化做出反应。随着尼古丁浓度的变化，nAChRs的数量分布在不同的功能状态(即激活、脱敏和长期失活状态)，这些状态可能是尼古丁介导的奖赏的基础，也有助于耐受和戒断的方面。在定量确定nAChRs介导的钙信号之后，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活性的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研究吸烟传递的尼古丁激活和减敏nAChRs的假说，nAChRs不断地分布在功能状态中。微岛培养和脑切片将被用于研究突变小鼠的组织，这是该计划项目申请的基本和统一的工具。这项工作最初将利用缺乏Alpha3、Alpha5、Alpha7或Beta2的突变小鼠，以及含有Alpha7(L247T)亚单位的小鼠，后者表现出减弱的脱敏作用。所有这些鼠标目前都是可用的。由于吸烟者大脑中nAChRs的数量增加，有观点认为，上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对于理解尼古丁成瘾的基础问题可能具有直接的重要意义。

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.