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.
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.
|Zhuang, Jianguo; Gao, Xiuping; Gao, Franklin et al. (2017) Mu-opioid receptors in the caudomedial NTS are critical for respiratory responses to stimulation of bronchopulmonary C-fibers and carotid body in conscious rats. Respir Physiol Neurobiol 235:71-78|
|Gao, Xiuping; Zhao, Lei; Zhuang, Jianguo et al. (2017) Prenatal nicotinic exposure prolongs superior laryngeal C-fiber-mediated apnea and bradycardia through enhancing neuronal TRPV1 expression and excitation. FASEB J 31:4325-4334|
|Zhuang, Jianguo; Gao, Peng; Pollock, Zemmie et al. (2016) Depressed Hypoxic and Hypercapnic Ventilatory Responses at Early Stage of Lethal Avian Influenza A Virus Infection in Mice. PLoS One 11:e0147522|
|Zhao, Lei; Zhuang, Jianguo; Zang, Na et al. (2016) Prenatal nicotinic exposure upregulates pulmonary C-fiber NK1R expression to prolong pulmonary C-fiber-mediated apneic response. Toxicol Appl Pharmacol 290:107-15|
|Lin, Ruei-Lung; Lin, Yu-Jung; Xu, Fadi et al. (2015) Hemorrhagic hypotension-induced hypersensitivity of vagal pulmonary C-fibers to chemical stimulation and lung inflation in anesthetized rats. Am J Physiol Regul Integr Comp Physiol 308:R605-13|
|Zhuang, Jianguo; Zhao, Lei; Zang, Na et al. (2015) Prenatal nicotinic exposure augments cardiorespiratory responses to activation of bronchopulmonary C-fibers. Am J Physiol Lung Cell Mol Physiol 308:L922-30|
|Lee, Lu-Yuan; Gu, Qihai; Xu, Fadi et al. (2013) Acid-sensing by airway afferent nerves. Pulm Pharmacol Ther 26:491-7|
|Zhang, Zhenxiong; Zhuang, Jianguo; Zhang, Cancan et al. (2013) Isoflurane depolarizes bronchopulmonary C neurons by inhibiting transient A-type and delayed rectifier potassium channels. Respir Physiol Neurobiol 186:164-72|
|Zhang, Zhenxiong; Zhuang, Jianguo; Zhang, Cancan et al. (2013) Isoflurane inhibits bronchopulmonary C-fiber-mediated apneic response to phenylbiguanide by depressing 5-HT3 receptor function in anesthetized rats. Neurosci Lett 552:1-4|
|Zhang, Zhenxiong; Zhang, Cancan; Zhuang, Jianguo et al. (2012) Contribution of central ?-receptors to switching pulmonary C-fibers-mediated rapid shallow breathing into an apnea by fentanyl in anesthetized rats. Brain Res 1469:73-81|
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