Genetics of Nicotine Tolerance: Role of Receptors

描述(由申请人提供)：最近对几个人类群体的分析发现了一些与吸烟行为相关的遗传标记，并对应于不同的nAChR亚基。这些研究有力地支持了受体亚单位结构或表达的遗传差异影响烟草使用的论点。然而，目前还没有确定哪些遗传差异鼓励和哪些不鼓励烟草使用。动物长期接触尼古丁，或人类长期接触烟草，都会导致耐受性和依赖性的形成。尼古丁最初的作用部位是烟碱胆碱能受体(NAChR)，其天然神经递质是乙酰胆碱。在大脑和外周有许多不同类型的nAChR。尼古丁与这些不同受体的相互作用不同，可能导致对药物的不同反应。众所周知，长期接触尼古丁还会改变一些尼古丁胆碱能受体(NAChR)的数量，甚至可能改变其功能。然而，慢性尼古丁暴露并不以相同的方式影响每一种nAChR亚型。小鼠将被作为模型生物来检验慢性尼古丁治疗的效果。尼古丁对小鼠的影响受到基因和特定nAChR基因缺失(敲除)或突变(敲除)的小鼠的影响。基因敲除和敲除小鼠将被用来研究尼古丁治疗引起的一些行为变化，主要是耐受性。此外，还将测量慢性尼古丁治疗对几种不同nAChR亚型表达和功能的影响。有两个具体目标。1422*nAChR在调节对慢性尼古丁的反应中的作用将在目标1中进行研究。1422*-nAChR是大脑中表达最高的亚型，长期尼古丁治疗会增加这些受体的数量。我们计划进行四种类型的实验来详细研究这种反应：a)测量基因完全缺失的14种敲除中的效果；b)测量14和22基因之一或两者部分缺失的小鼠的反应；c)测量表达使这些受体变得超敏的突变的小鼠的反应；d)评估与1422-nAChR选择性相互作用的药物的治疗效果。15和24亚基在调节慢性尼古丁反应中的作用将在目标2中进行研究。15很有趣，因为它是与烟草使用最密切相关的nAChR基因，而24是有趣的，因为nAChR结合了这个亚基影响尼古丁戒断，可能会降低耐受性的形成。15只和24只零突变和杂合子小鼠的反应将与野生型小鼠的反应进行比较。这些研究的结果将为主要尼古丁受体亚型的调节以及另外两种亚型在慢性尼古丁引起的变化中的作用提供新的信息。这些结果还可以帮助识别对慢性尼古丁的特定行为和生化反应，这些反应是由被认为是人类吸烟重要因素的基因介导的。长期使用尼古丁或烟草会改变人类和实验动物体内特定尼古丁结合分子(受体)的数量。我们将研究慢性尼古丁治疗在表达较少或不同受体的小鼠中引起的反应，以确定这些分子差异如何影响尼古丁依赖的各个方面。

DESCRIPTION (provided by applicant): Recent analyses of several human populations have identified a number of genetic markers which correlate with aspects of smoking behavior and that correspond to different nAChR subunits. These studies strongly support the contention that genetic differences in receptor subunit structure or expression influence tobacco use. However, it has not been established which of the genetic differences encourage and which discourage tobacco use. Chronic exposure of animals to nicotine, or of humans to tobacco, results in the development of tolerance and dependence. The initial sites of action of nicotine are the nicotinic cholinergic receptors (nAChR), for which the native neurotransmitter is acetylcholine. There are many different types of nAChR in the brain and in the periphery. Nicotine's interaction with these various receptors differs and can lead to different responses to the drug. It is well established that chronic nicotine exposure also changes the number, and perhaps the function, of some nicotinic cholinergic receptors (nAChR). However, chronic nicotine exposure does not affect each nAChR subtype in the same way. Mice will be used as the model organism to examine effects of chronic nicotine treatment. The effects of nicotine in mice are influenced by genotype and mice from which a specific nAChR gene has been deleted (knockout) or mutated (knockin) have been generated. The knockout and knockin mice will be used to investigate some behavioral changes induced by nicotine treatment, primarily tolerance. Furthermore, the effects of chronic nicotine treatment on the expression and function of several different nAChR subtypes will be measured. There are two specific aims. The role of 1422*nAChR in modulating response to chronic nicotine will be investigated in Aim 1. 1422*- nAChR is the most highly expressed subtype in the brain and chronic nicotine treatment increases the number of these receptors. We plan four types of experiments to study this response in detail a) measure effects in 14 knockouts, where the gene is completely gone; b) measure the response in mice in which either or both 14 and 22 genes have been partially deleted; c) measure response in mice expressing mutations that make these receptors hypersensitive; and d) evaluate the effects of treatment with a drug that interacts selectively with 1422-nAChR. The role of the 15 and 24 subunits in modulating responses to chronic nicotine will be investigated in Aim 2. 15 is interesting because it is the nAChR gene that most robustly correlates with tobacco use, while 24 is interesting because nAChR incorporating this subunit affect nicotine withdrawal and may diminish tolerance development. Response of 15 and 24 null mutant and heterozygote mice will be compared to that of wild-type mice. The results of these studies will provide new information on the regulation of the major nicotinic receptor subtype and the contribution of two other subtypes to changes induced by chronic nicotine. The results could also help identify specific behavioral and biochemical responses to chronic nicotine mediated by genes identified as important factors in human smoking. Chronic use of nicotine or tobacco changes the amount of the specific nicotine-binding molecules (receptors) in both humans and laboratory animals. We will study the responses that chronic nicotine treatment elicits in mice that express fewer or different receptors to determine how these molecular differences affect aspects of nicotine dependence.