Effect of Prenatal Nicotinic Exposure on Control of Hypoxic Ventilatory Response

描述(申请人提供)：婴儿猝死综合症(SIDS)是导致婴儿死亡的主要原因。香烟烟雾(尼古丁暴露)是关键的危险因素，低氧血症是小岛屿发展中国家的急性先兆。尽管小岛屿发展中国家的发病机制尚不清楚，但抑制的缺氧性呼吸系统反应(DHVR)被认为是主要因素。已有的传统产前尼古丁暴露(TPNE)诱导的SIDS动物模型显示，在60min的严重缺氧期间，大鼠幼鼠的死亡率过高(15%)。该项目的目标1是通过使用一个更现实的“完整”PNE(FPNE)来改进这一模型，该PNE由怀孕前、怀孕期间和哺乳期组成，以最大限度地增加PNE对心肺功能的不利影响。此外，还将进一步明确dHVR在死亡率中的因果作用和dhvr的中心起源。最近，我们发现灭活支气管肺C受体(PCF)可以独特地消除在肺部炎症大鼠中观察到的dHVR，这表明PCF在病理条件下钝化HVR中起着关键作用。据报道，PCF被香烟烟雾(尼古丁)敏化，并被低氧产物腺苷(AD)刺激，主要是通过作用于A1受体(A1R)。这些发现，以及SIDS患者迷走神经C纤维的增加，导致了目标2，在我们的模型中，我们将确定fPNE诱导的dHVR和死亡是否依赖于AD刺激的PCF，以及在我们的模型中，fPNE是否主要通过增加PCF的数量和A1 R来增强PCF对缺氧(AD)的反应。一般认为，PCF的激活通过释放谷氨酸，通过作用于AMPA受体(AMPAR)刺激PCF驱动的神经元(MNTS)，从而抑制呼吸。这种抑制作用被作用于神经激肽1受体(NK1R)的局部P物质(SP)放大。最重要的是，局部SP的释放是通过低氧刺激颈动脉小体而介导的，并且在SIDS患者中显著升高。由于fPNE上调mNTS NK1R的表达，目标3的研究将确定fPNE是否促进NK1R和SP的合成，以及缺氧诱导的mNTS中SP的释放，通过SP促进AMPAR介导的神经元活动，集中增强PCF驱动的神经元活动，导致dHVR。拟议的研究将通过电生理学、药理学、免疫细胞化学和分子方法在大鼠幼鼠身上进行。我们在《目标》中描述的预测结果将：1)对PCF的可塑性和PCF在出生后发育期间和病理条件下控制呼吸的作用产生新的概念；2)对吸烟(PNE)和低氧血症(如SID)等疾病固有的呼吸系统疾病的发病机制有新的见解；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：我们将在一种新的小岛屿发展中国家动物模型中确定低氧呼吸反应抑制(DHVR)在观察到的死亡率中所起的关键作用，并进一步阐明这种dVHR的外周和中枢机制。这些研究将拓宽我们对呼吸病理生理学的认识，产生关于小岛屿发展中国家发病的新概念，最重要的是，可能突出预防和治疗干预小岛屿发展中国家患者呼吸衰竭的新目标。

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.