Nicotinic Acetylcholine Receptor Mediated Bitter Taste Transduction

描述（由申请人提供）：每年有超过500万人主要死于与吸烟有关的肺癌。烟草含有尼古丁，这是导致强烈吸烟成瘾的主要化合物。 尼古丁是成瘾性的，因为它对烟碱乙酰胆碱受体（nAChR）介导的中枢神经系统的影响。 由于味觉受体基因（T2 R38）中的多态性而感知苯硫脲的苦味的能力保护受试者免于发展成吸烟成瘾并减少来自吸烟的正强化。这表明味觉的变化在吸烟的背景下起着重要作用，并提供了涉及尼古丁成瘾的重要线索。虽然尼古丁被描述为苦味，但编码尼古丁味道的分子和细胞机制仍不清楚。我们的研究表明，尼古丁通过两个平行的受体介导的途径激活味觉系统。 一种途径涉及G蛋白偶联受体（T2 R）和下游效应物（G蛋白味觉蛋白，酶PLC 2和阳离子通道TRPM 5），这些都是甜味，苦味和鲜味苦味感知所共有的。第二个途径利用nAChR，并对尼古丁、乙酰胆碱、乙醇和其他可能的苦味促味剂做出反应，并且对于它们的完整感觉表征是必不可少的。本研究的总体目标是增加我们对不同nAChR亚基对尼古丁、乙酰胆碱、乙醇和其他苦味化合物苦味的贡献的理解。 研究旨在探讨不同的nAChR亚基的存在下，味蕾细胞使用分子技术（RT-PCR，定量RT-PCT，免疫组织化学和原位杂交）。为了研究nAChRs在外周味觉传导中的作用，我们将使用全细胞膜片钳技术监测nAChRs的药理学激动剂和拮抗剂对单个分离的味觉细胞、鼓索味觉神经反应和舔率的影响，舔率作为对尼古丁、乙酰胆碱、乙醇和其他苦味剂。 具体而言，我们将使用基因修饰小鼠，其中特定的nAChR亚基基因或TRPM 5阳离子通道基因已被删除。本研究中获得的关于nAChR依赖性苦味感知通路的信息可以为我们提供关于可能参与尼古丁和酒精成瘾或预测尼古丁和酒精成瘾的味觉相关事件的信息。吸烟对食物消耗和味觉偏好的影响可能发生于外周味觉调节，这是由于长期暴露于作用于味蕾中的nAChR的尼古丁以及其他因素。 公共卫生相关性：味觉的改变在吸烟和酗酒的背景下起着重要的作用，并提供了与其成瘾有关的重要线索。因此，重要的是要了解编码尼古丁和乙醇苦味的分子和细胞机制。 我们的研究表明，烟碱乙酰胆碱受体提供了另一种苦味感知机制，该机制与TRPM 5依赖性转导途径并行工作，并且对于尼古丁、乙醇和其他促苦味剂的苦味的完整表示是必要的。

DESCRIPTION (provided by applicant): Every year, more than 5 million people die primarily from developing smoking related lung cancer. Tobacco contains nicotine, the major compound responsible for driving the strong addiction to smoking. Nicotine is addictive because of its effects on the central nervous system mediated by nicotinic acetylcholine receptors (nAChRs). The ability to sense the bitter taste of phenylthiocarbamide due to polymorphisms in a taste receptor gene (T2R38) protects a subject from developing a cigarette smoking addiction and reduces the positive reinforcement from smoking. This suggests that changes in taste play a significant role in the context of cigarette smoking and provide important cues involved in nicotine addiction. Although nicotine is described as bitter tasting, the molecular and cellular mechanisms that encode the taste of nicotine remain unclear. Our studies show that nicotine activates the taste system via two parallel receptor-mediated pathways. One pathway involves a G-protein coupled receptor (T2R) and down stream effectors (a G-protein gustducin, an enzyme PLC¿2 and a cation channel, TRPM5) that are common to sweet, bitter and umami bitter sensing. The second pathway utilizes nAChRs and responds to nicotine, acetylcholine, ethanol and perhaps other bitter tastants and is essential for their complete sensory representation. The overall aim of this study is to increase our understanding of the contribution of different nAChR subunits to the bitter taste of nicotine, acetylcholine, ethanol and other bitter compounds. Studies are designed to investigate the presence of different nAChR subunits in taste bud cells using molecular techniques (RT-PCR, quantitative-RT-PCT, immunohistochemical and in situ hybridization). To investigate the role of nAChRs in peripheral taste transduction we will monitor the effects of pharmacological agonists and antagonists of nAChRs on single isolated taste cells using whole cell patch clamp technique, chorda tympani taste nerve responses and on lick rates as a measure of altered behavioral responses to nicotine, acetylcholine, ethanol and other bitter tastants in several animal models. Specifically, we will use genetically modified mice in which specific nAChR subunit genes or genes for TRPM5 cation channel have been deleted. The information obtained in this study on the nAChR-dependent bitter- sensing pathway may provide us with information regarding taste-related events that may be either involved in or predictors of nicotine and alcohol addiction. The effects of cigarette smoking on food consumption and taste preferences may occur from peripheral taste modulation due to chronic exposure to nicotine acting on nAChRs in taste buds among other factors. PUBLIC HEALTH RELEVANCE: Alterations in taste play a significant role in the context of cigarette smoking and alcohol abuse and provide important cues involved in their addiction. Therefore, it is important to understand the molecular and cellular mechanisms that encode the bitter taste of nicotine and ethanol. Our studies indicate that nicotinic acetylcholine receptors provide another bitter sensing mechanism that works in parallel with the TRPM5- dependent transduction pathway and is necessary for the complete representation of the bitter taste of nicotine, ethanol and perhaps other bitter tastants.