Responsiveness to nicotine of nucleus tractus solitarius neurons

描述(申请人提供)：孤束核(NTS)是一组功能和解剖上不同的细胞，是调节自主神经功能的主要处理部位。NTS的神经元接收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的突触前和突触后神经回路接受密集的胆碱能神经支配，并表达功能性烟碱型乙酰胆碱受体(NAChRs)。麻醉大鼠静脉注射尼古丁可降低胃动力，这种作用可被双侧迷走神经切断显著抑制，提示NTS和其他脑干背侧迷走神经复合体(DVC)核团的功能性nAChRs参与了胃肠反射。尽管NTS具有异质性，但它包含功能特异的NTS细胞的离散亚群。然而，突触前和突触后胆碱能对功能特异的NTS通路的控制尚不清楚。以前的研究和本实验室的最新初步数据表明，根据NTS尾侧细胞的形态、细胞化学特性、传入输入和轴突靶标，在突触前和突触后存在选择性的尼古丁效应。具体地说，已经观察到尼古丁对突触释放谷氨酸的强烈促进作用，在尾侧NTS神经元(这些神经元将被称为对尼古丁的突触前反应)投射到或通过关键的胃肠控制核-迷走神经的背侧运动核，但不投射到臂旁核，臂旁核是上行自主神经和味觉纤维到达高级脑中枢的主要靶点。根据初步结果，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特定尾侧NTS细胞亚群受选择性突触前和躯体树突nAChRs亚型的不同调控。拟议的实验旨在：1)将尼古丁的作用与NTS尾侧神经元亚群的投射靶点联系起来，使用体内和体外逆行示踪剂注射结合膜片钳电生理学来鉴定(目标1)；以及2)确定尼古丁对NTS脑干切片潜在影响的细胞和突触机制(目标2)。了解nAChR亚型在尼古丁类药物对NTS尾侧神经元功能特异性亚群影响的机制和药理学，将有助于我们更好地了解nAChRs在胃和其他内脏信息的处理和整合中的作用。这可能导致开发新的治疗策略，选择性地靶向特定的尼古丁反应自主神经通路(例如，胃肠道)。拟议研究的结果可能会扩大现有的治疗选择，旨在改善消化健康和治疗消化疾病，如肥胖和厌食症。与公共健康相关：尼古丁改变大脑中调节胃肠道系统的神经元的活动，对喂养和消化至关重要，但这是如何发生的在很大程度上尚不清楚。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控制肠道的方式，这些机制就是这项提议的主题。这里的实验将指出利用尼古丁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.