Responsiveness to nicotine of nucleus tractus solitarius neurons

描述（由申请人提供）：孤束核（NTS）是一组功能和解剖学上异质的细胞，作为调节自主神经功能的主要处理部位。NTS的神经元接受内脏感觉和味觉信号，并将信息传递到内脏运动和其他脑区。乙酰胆碱是一种主要的自主神经递质，NTS中的突触前和突触后神经元回路接受密集的胆碱能神经支配并表达功能性烟碱乙酰胆碱受体（nAChR）。麻醉大鼠静脉注射尼古丁可降低胃运动，双侧迷走神经切断术可显著抑制这种效应，表明NTS和脑干背侧迷走神经复合体（DVC）其他核团的功能性nAChR参与胃肠反射。尽管其异质性，NTS包含功能特异性NTS细胞的离散子集。然而，突触前和突触后胆碱能控制功能特异性NTS途径是未知的。以前的研究和最近的初步数据表明，有选择性的突触前和突触后烟碱的影响，尾侧NTS细胞的特定子集所定义的形态，细胞化学特性，传入输入，和轴突的目标。具体而言，在尾侧NTS神经元（这些神经元将被称为对尼古丁有突触前反应）的一个子集中观察到尼古丁对谷氨酸的突触释放的强烈增强，这些神经元投射到或通过关键的胃肠控制核（迷走神经背侧运动核），但不投射到臂旁核，臂旁核是上行自主神经和味觉纤维到达高级大脑中心的主要靶点。基于初步结果，我们假设，特定的子集的尾部NTS细胞与定义的形态，生理，脑干投射或功能内脏目标的差异调节突触前和体树突nAChRs的选择性亚型。拟议的实验旨在：1）将尼古丁的作用与尾侧NTS神经元亚群的投射靶点联系起来，通过体内和离体注射逆行示踪剂结合膜片钳电生理学进行鉴定（目的1）; 2）鉴定尼古丁在NTS脑干切片中潜在作用的细胞和突触机制（目的2）。了解nAChR亚型的机制和药理学基础上的烟碱剂对功能特异性亚群的尾侧NTS神经元的影响，将提高我们的nAChR在胃和其他内脏信息的处理和整合的作用的知识。这可能导致开发新的治疗策略，用于选择性靶向特定的尼古丁响应性自主通路（例如，胃肠道）。拟议研究的结果可以扩大现有的治疗选择，旨在改善消化系统健康和治疗消化系统疾病，如肥胖和厌食症。公共卫生相关性：尼古丁会改变大脑中调节胃肠道系统的神经元的活动，这些神经元对进食和消化至关重要，但这是如何发生的在很大程度上是未知的。我们已经发现了尼古丁调节一小部分神经元的强大手段的证据，这些神经元影响大脑如何控制肠道，这些机制就是本提案的主题。这里的实验将指出使用烟碱机制来改变与进食相关的胃肠道系统功能的新方法。

DESCRIPTION (provided by applicant): The nucleus of the solitary tract (NTS) is a functionally and anatomically heterogeneous group of cells that serves as a principle processing site regulating autonomic functions. Neurons of the NTS receive visceral sensory and gustatory signals and relay the information to visceral motor and other brain areas. Acetylcholine is a major autonomic neurotransmitter and the pre- and postsynaptic neuronal circuitry in the NTS receives a dense cholinergic innervation and expresses functional nicotinic acetylcholine receptors (nAChRs). Intravenous administration of nicotine in anesthetized rats decreases gastric motility and this effect could be significantly suppressed by bilateral vagotomy, indicating the involvement of functional nAChRs of the NTS and other nuclei of the brainstem dorsal vagal complex (DVC) in gastrointestinal reflexes. Despite its heterogeneity, the NTS contains discrete subsets of functionally-specific NTS cells. However, the pre- and postsynaptic cholinergic control of functionally-specific NTS pathways is unknown. Previous studies and recent preliminary data from this laboratory indicate that there are selective pre- and postsynaptic nicotinic effects on specific subsets of caudal NTS cells as defined by their morphology, cytochemical identity, afferent input, and axonal targets. Specifically, a robust enhancement of synaptic release of glutamate by nicotine has been observed in a subset of caudal NTS neurons (these will be referred to as presynaptically-responsive to nicotine) projecting to or through the key gastrointestinal control nucleus, the dorsal motor nucleus of the vagus, but not to the parabrachial nucleus, a primary target for the ascending autonomic and gustatory fibers to higher brain centers. Based on preliminary results, we hypothesize that specific subsets of caudal NTS cells with defined morphology, physiology, and brainstem projection or functional visceral target are differentially regulated by selective subtypes of presynaptic and somatodendritic nAChRs. Proposed experiments aim to: 1) relate nicotine's effects to the projection targets of subsets of caudal NTS neurons, identified using in vivo and ex vivo injections of retrograde tracers combined with patch-clamp electrophysiology (Aim 1); and 2) identify the cellular and synaptic mechanisms of underlying effects of nicotine in NTS brainstem slices (Aim 2). Understanding the mechanisms and pharmacology of nAChR subtypes underlying the effects of nicotinic agents on function- specific subsets of caudal NTS neurons will enhance our knowledge of the role of nAChRs in the processing and integration of gastric and other visceral information. This may result in the development of new therapeutic strategies for selective targeting of specific nicotine-responsive autonomic pathways (e.g., gastrointestinal). Results from the proposed studies could expand available therapeutic options aimed at improving digestive health and treatments of digestive disorders, such as obesity and anorexia. PUBLIC HEALTH RELEVANCE: Nicotine changes the activity of neurons in the brain that regulate the gastrointestinal system and are critical to feeding and digestion, but how this occurs is largely unknown. We have uncovered evidence of a powerful means for nicotine to regulate a small set of neurons that influence how the brain controls the gut, and these mechanisms are the topic of this proposal. The experiments here will point to new ways of using nicotinic mechanisms to modify functions of the gastrointestinal system associated with feeding.