Effect of Prenatal Nicotinic Exposure on Control of Hypoxic Ventilatory Response

描述（申请人提供）：婴儿猝死综合征（SIDS）是婴儿死亡的主要原因。吸烟（尼古丁暴露）是关键的危险因素，低氧血症是SIDS的急性前兆。虽然小岛屿发展中国家的致病机制知之甚少，一个压抑的缺氧反应（dHVR）已被认为是一个主要的球员。现有的SIDS动物模型诱导的传统产前尼古丁暴露（TPNE）已显示出过度的死亡率（15%），在60分钟的严重缺氧的大鼠幼崽。该项目的目的1是通过使用更现实的“足月”PNE（fPNE）来改进该模型，该模型包括妊娠前和妊娠期及哺乳期，以最大限度地提高PNE对心肺功能的不利影响。此外，将进一步确定dHVR在死亡率中的因果作用和dHVR的中心起源。最近，我们发现支气管肺C-firers（PCF）的失活独特地消除了肺部炎症大鼠中观察到的dHVR，这表明PCF在病理条件下在钝化HVR方面发挥着关键作用。据报道，PCF被香烟烟雾（尼古丁）致敏，并主要通过作用于A1受体（A1 R）而被缺氧产物腺苷（AD）刺激。这些发现，沿着SIDS受害者迷走神经C纤维增加，导致目标2，其中我们将确定fPNE诱导的dHVR和死亡是否依赖于AD刺激PCF，以及fPNE是否主要通过增加我们模型中PCF的数量和A1 R来放大PCF对缺氧（AD）的反应。目前普遍认为，多光子晶体纤维激活后通过释放谷氨酸抑制通气，谷氨酸通过作用于AMPA受体（AMPAR）刺激孤束核尾侧和中间核（mNTS）内的多光子晶体纤维驱动神经元。这种抑制作用通过局部P物质（SP）作用于神经激肽1受体（NK 1 R）而放大。最重要的是，局部SP释放是由颈动脉体的缺氧刺激介导的，并且在SIDS受害者中大大升高。由于fPNE上调mNTS NK 1 R表达，目的3中的研究将确定fPNE是否促进NK 1 R和SP合成以及mNTS中缺氧诱导的SP释放，以通过SP促进AMPAR介导的神经元活性来集中增强PCF驱动的神经元活性，从而导致dHVR。将采用电生理学、药理学、免疫细胞化学和分子方法在大鼠幼仔中进行拟定研究。本研究的目的是：1）对PCFs的可塑性及其在出生后发育和病理状态下呼吸控制中的作用提出新的概念; 2）对吸烟和低氧血症相关疾病（如SIDS）中呼吸系统疾病的发病机制有新的认识;以及3）帮助我们为这些患者开发新的预防策略和药物治疗。 公共卫生相关性：我们将建立一个关键的作用，一个压抑的缺氧反应（dHVR）中观察到的死亡率在一个新的SIDS动物模型，并进一步阐明这种dVHR的外周和中枢机制。这些研究将扩大我们的呼吸病理生理学知识，产生一个新的概念，小岛屿发展中国家的成因，最重要的是，可能会突出新的目标，预防和治疗干预呼吸衰竭的小岛屿发展中国家的受害者。

DESCRIPTION (provided by applicant): Sudden infant death syndrome (SIDS) is a leading cause of infant mortality. Cigarette smoke (nicotinic exposure) is the key risk factor and hypoxemia is an acute precursor for SIDS. Although the pathogenic mechanisms of SIDS are poorly understood, a depressed hypoxic ventilatory response (dHVR) has been assumed to be a major player. An existing SIDS animal model induced by traditional prenatal nicotinic exposure (tPNE) has shown an excessive mortality (15%) during 60 min severe hypoxia in rat pups. Aim 1 of this project is to improve this model by using a more realistic "full-term" PNE (fPNE) that consists of the period before pregnancy and during pregnancy and lactation to maximize adverse impacts of PNE on cardiorespiratory functions. In addition, the causal role of the dHVR in the mortality and the central origin of the dHVR will be further defined. Recently, we found that inactivation of bronchopulmonary C-firers (PCFs) uniquely eliminated the dHVR observed in rats with pulmonary inflammation, suggesting a critical role of PCFs in blunting the HVR under pathological condition. PCFs are reportedly sensitized by cigarette smoke (nicotine) and stimulated by the hypoxic product adenosine (AD) mainly via acting on A1 receptor (A1R). These findings, along with increased vagal C-fibers in SIDS victims, lead to Aim 2, in which we will determine if fPNE-induced dHVR and death depend on AD stimulating PCFs and if fPNE amplifies the PCF response to hypoxia (AD) mainly via increasing PCFs' population and A1Rs in our model. It is generally accepted that activation of PCFs inhibits ventilation via releasing glutamate that stimulates PCF-driven neurons in the caudal and middle nucleus tractus solitarius (mNTS) via acting on AMPA receptor (AMPAR). This inhibition is amplified by local substance P (SP) acting on neurokinin 1 receptor (NK1R). Most importantly, local SP release is mediated by hypoxic stimulation of the carotid body and is greatly elevated in SIDS victims. Because fPNE upregulates mNTS NK1R expression in our pilot data, studies in Aim 3 will define if fPNE promotes NK1R and SP synthesis and the hypoxia-induced SP release in the mNTS to centrally augment PCF-driven neuronal activity via SP facilitating AMPAR-mediated neuronal activity, leading to the dHVR. The proposed studies will be performed in rat pups by using electrophysiological, pharmacological, immunocytochemical, and molecular approaches. Our predicted results as described in the aims will: 1) generate a new concept of PCFs' plasticity and PCFs' role in control of breathing during postnatal development and under pathological condition; 2) gain new insight into the mechanisms underlying the pathogenesis of respiratory disorders inherent in the diseases involving cigarette smoking (PNE) and hypoxemia, such as SIDS; and 3) help us to develop new preventive strategies and pharmacological therapies for these patients. PUBLIC HEALTH RELEVANCE: We will establish the key role a depressed ventilatory response to hypoxia (dHVR) plays in the mortality observed in a new SIDS animal model and further elucidate the peripheral and central mechanisms underlying this dVHR. These studies will broaden our knowledge of respiratory pathophysiology, yield a new concept of SIDS genesis and, most importantly, may highlight new targets for preventing and therapeutically intervening in the respiratory failure in SIDS victims.