CNS Pathways Integrating Respiratory and Metabolic Control

描述（由申请人提供）：维持动脉血气和酸碱平衡需要代谢的变化与肺泡通气的比例变化相匹配。瘦素是一种细胞因子激素，在能量平衡中起着核心作用，并被认为是小鼠和人类通气与代谢匹配的重要因素。这在临床上具有相关性，例如，一部分肥胖者对瘦素和低通气有抵抗性，同时动脉PCO2升高和动脉PO2降低（肥胖低通气综合征，OHS）。人们普遍认为瘦素通过中枢神经系统机制刺激呼吸。然而，中枢神经系统内的多个核含有表达瘦素受体的神经元（称为LepRb神经元），并且几乎没有证据表明哪一组神经元参与了呼吸刺激。根据前期研究和文献，我们假设脑干和下丘脑的多个特定组的LepRb神经元参与了呼吸刺激。此外，多肽递质/调节剂与许多这些细胞群有关，这些途径中活性的药理学操作可以为未来临床相关药理学操作这些途径活性的发展提供基础。将讨论三个具体目标。在Aim 1中，我们将利用Cre-loxP技术和光遗传学激活或沉默转基因小鼠中的特定LepRb神经元群。对特定LepRb神经元群的选择性激活反应的呼吸刺激将提示其在呼吸中的作用。神经活性标记物c-Fos的免疫组化将用于识别可能作为传递核参与特异性途径的细胞群

DESCRIPTION (provided by applicant): Maintenance of arterial blood gas and acid-base homeostasis requires that a change in metabolism be matched by a proportional change in alveolar ventilation. Leptin, a cytokine hormone, has a central role in energy balance and has been implicated as an important contributor to the matching of ventilation to an aspect of metabolism in both mice and humans. This is clinically relevant as, for example, a subset of obese humans is resistant to leptin and hypoventilate with both an increase in arterial PCO2 and decrease in arterial PO2 (obesity hypoventilation syndrome, OHS). It is generally believed that leptin stimulates breathing through a CNS mechanism. However, multiple nuclei within the CNS contain leptin receptor expressing neurons (termed LepRb neurons) and there is almost no evidence as to which groups are involved in the stimulation of breathing. Based on preliminary studies and the literature we hypothesize that multiple specific groups of brainstem and hypothalamic LepRb neurons contribute to the respiratory stimulation. Additionally, peptide transmitters/modulators have been associated with many of these cell groups and pharmacologic manipulation of activity in these pathways could provide the basis for future development of clinically relevant pharmacological manipulation of activity in these pathways. Three Specific Aims will be addressed. In Aim 1, we will take advantage of Cre-loxP technology and optogenetic activation or silencing of specific LepRb neuronal groups in transgenic mice. Stimulation of breathing in response to selected activation of a specific LepRb neuronal group will suggest a role in breathing. Immunohistochemistry for the neuronal activity marker, c-Fos, will be used to identify cell groups that may participate as relay nuclei in pathways from specific LepRb neuronal groups to the CNS respiratory circuits. This potential role will be tested by using systemic leptin administration to stimulate breathing while determining whether bilateral inactivation of the target nucleus reduces the respiratory stimulation. In Aim 2, we will combine standard retrograde tracing with a novel transynaptic viral tracing method that crosses only 1 synapse to specify leptin-activated mono- and poly-synaptic pathways stimulating breathing. The peptide transmitters contained within these pathways will be identified immunohistochemically. In Aim 3, in vitro studies will define the impact of peptide transmitters within the leptin pathways on brainstem respiratory neurons and identify the cellular/molecular mechanisms underlying their influence. The combined studies will systematically identify CNS LepRb neuronal groups that stimulate breathing in response to systemic leptin administration. Additionally, paucisynaptic pathways mediating this influence will be revealed as will the identity of their peptide transmitters. Moreover, associated cellular/molecular mechanisms contributing to a stimulation of breathing will be defined. The findings could form the basis for the future development of pharmacotherapies for OHS patients.