Responsiveness to nicotine of nucleus tractus solitarius neurons

描述（由申请人提供）：孤立束核（NTS）是一个功能和解剖学上异质性的细胞群，是调节自主神经功能的主要加工部位。NTS的神经元接收内脏感觉和味觉信号，并将信息传递给内脏运动和其他大脑区域。乙酰胆碱是一种主要的自主神经递质，NTS突触前和突触后神经元回路接受密集的胆碱能神经支配，并表达功能性烟碱胆碱受体（nAChRs）。麻醉大鼠经静脉给药后胃运动减弱，双侧迷走神经切断可明显抑制这一作用，提示NTS和脑干迷走神经背复合体（DVC）其他核的功能性nachr参与了胃肠道反射。尽管其异质性，NTS包含功能特异性NTS细胞的离散子集。然而，功能特异性NTS通路的突触前和突触后胆碱能控制尚不清楚。本实验室先前的研究和最近的初步数据表明，根据其形态、细胞化学特性、传入输入和轴突靶点的定义，对尾侧NTS细胞的特定亚群存在选择性的突触前和突触后尼古丁作用。具体来说，尼古丁对突触释放谷氨酸的增强作用已经在尾侧NTS神经元的一个亚群（这些神经元被称为突触前对尼古丁有反应）中被观察到，这些神经元投射到或通过关键的胃肠道控制核，迷走神经的背侧运动核，但不投射到臂旁核，臂旁核是上行的自主神经和味觉纤维到高级脑中心的主要目标。基于初步结果，我们假设具有明确形态、生理和脑干投射或功能内脏靶点的尾侧NTS细胞的特定亚群受到突触前和体树突nachr的选择性亚型的差异调节。拟议的实验旨在：1)将尼古丁的作用与尾侧NTS神经元亚群的投射目标联系起来，这些目标是通过体内和体外注射逆行示踪剂结合膜片钳电生理学（aim 1）确定的；2)确定尼古丁在NTS脑干切片中潜在作用的细胞和突触机制（Aim 2）。了解nAChR亚型的机制和药理学，以及烟碱对尾端NTS神经元功能特异性亚群的影响，将增强我们对nAChR在胃和其他内脏信息的加工和整合中的作用的认识。这可能会导致新的治疗策略的发展，选择性靶向特定的尼古丁反应自主神经通路（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：尼古丁改变大脑中调节胃肠系统的神经元的活动，对进食和消化至关重要，但这是如何发生的还不得而知。我们已经发现了证据，证明尼古丁有一种强大的手段来调节一小部分神经元，这些神经元影响大脑控制肠道的方式，这些机制就是本提案的主题。这里的实验将指出利用尼古丁机制来改变与进食有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.