Nicotine Modulation of Parasympathetic Cardiac Neurons

描述（由申请人提供）：三叉心反射和潜水反射是最强大的自主反射之一。对三叉神经进行电刺激或机械刺激会引起包括人类在内的动物心率急剧下降，在临床文献中通常被称为“三叉神经心脏反射”，在动物研究中被称为“三叉神经抑制反应”。三叉心反射的一个子集是跳水反射。将鼻黏膜暴露在水或空气中的化学刺激物中刺激潜水反射会引起明显的心动过缓，单次面部浸泡后心率下降高达51%。然而，过度的跳水反射与婴儿猝死综合征（SIDS）有关。小岛屿发展中国家是1个月至1岁婴儿死亡的主要原因。小岛屿发展中国家的最高风险因素之一是吸烟，而烟草烟雾除了尼古丁外还含有许多有害物质，尼古丁在小岛屿发展中国家尤其值得关注，因为它能够穿过胎盘并集中在胎儿体内，而产前暴露于尼古丁会损害新生动物从心肺疾病中复苏的能力。本项目将直接测试三叉神经和潜水反射中感觉神经元的激活刺激心脏迷走神经元的假设，这些反射途径是内源性的，由烟碱和毒碱胆碱能受体进行差异调节，确定这种调节发生在反射途径的哪个位置，最后确定胎儿暴露于尼古丁是否会夸大心脏迷走神经元的兴奋。为了验证这些假设，我们将使用在该领域相当新颖的技术。这两种新方法包括利用慢病毒表达增强黄色荧光蛋白（eYFP）鉴定源自鼻粘膜的感觉神经元的突触末梢，以及表达通道视紫红质-2 (ChR2)，一种光激活的阳离子通道，选择性地光激活这些鼻感觉神经元的纤维和突触末梢。

DESCRIPTION (provided by applicant): The trigeminocardiac and diving reflexes are among the most powerful autonomic reflexes. Electrical or mechanical stimulation of the trigeminal nerve evokes a dramatic decrease in heart rate in animals including man, and has often been termed the `trigeminocardiac reflex' in the clinical literature, and `trigeminal depressor responses' in animal studies. A subset of the trigeminocardiac reflex is the diving reflex. Stimulation of the diving reflex by exposing the nasal mucosa to water or air-borne chemical irritants evokes a pronounced bradycardia with heart rate decreasing up to 51% upon a single facial submersion. However an exaggerated diving reflex has been implicated in sudden infant death syndrome (SIDS). SIDS is the leading cause of death among infants who are 1 month to 1 year old. One of the highest risk factors for SIDS is cigarette smoking and while tobacco smoke contains a number of deleterious agents in addition to nicotine, nicotine is of particular concern in relation to SIDS due to its ability to cross the placenta and concentrate in the fetus, and prenatal nicotine exposure impairs the ability of newborn animals to resuscitate from cardiorespiratory challenges. This project will directly test the hypotheses that activation of sensory neurons in the trigeminocardiac and diving reflexes excites cardiac vagal neurons, these reflex pathways are endogenously and differentially modulated by nicotinic and muscarinic cholinergic receptors, determine where in this reflex pathway this modulation occurs, and finally whether fetal exposure to nicotine exaggerates this excitation of cardiac vagal neurons. To test these hypotheses we will utilize techniques that are quite novel to this field. Two such new approaches include the identification of the synaptic terminals of sensory neurons originating in the nasal mucosa using lentivirus expression of enhanced yellow fluorescent protein (eYFP), as well as the expression of channelrhodopsin-2 (ChR2), a light activated cation channel, to selectively photoactivate the fibers and synaptic terminals of these nasal sensory neurons.