The Ventral Medulla and the Sudden Infant Death Syndrome

描述(申请人提供)：尽管回归睡眠运动取得了成功，但婴儿猝死综合症(SIDS)仍然是当今美国新生儿后死亡的主要原因。该计划项目在上一个周期的主要发现是，延髓5-羟色胺(5-HT)系统的多种发育异常与小岛屿发展中国家有关。这些人类在项目1中的发现已经导致在项目2-4中，延髓5-羟色胺系统在动物模型中多种稳态功能的状态相关调节中发挥关键作用。此外，它们还在项目5中在脑干5-羟色胺系统的分子水平上建立了发育概况。这些发现为拟议的第三周期带来了以下压倒一切的假说：SID的一个重要子集是由于延髓5-羟色胺系统和相关神经调节系统的发育障碍，这些系统在产前发生，但它在出生后发挥作用-在新生儿过渡到宫外生命的前6个月，经历维持独立动态平衡的回路成熟，是SIDS的最大风险。这种疾病损害了对可能威胁生命的、但在婴儿睡眠期间经常发生的应激源的保护性稳态反应，这些应激源反过来会导致体内平衡失调(缺氧、高碳酸血症)，每种疾病本身都可能不致命，但它们结合在一起会导致死亡。我们的目标是：1)确定多种递质/调节剂在小婴儿神经化学延髓病理中的作用；2)在啮齿动物模型中确定动态平衡应激源--单独和联合--对不同睡眠状态、不同性别和不同年龄的自主神经和呼吸功能的影响；3)确定慢性间歇性低氧在增强小儿麻痹症脑干病理中的作用；4)在动物模型中确定γ-氨基丁酸(GABA)、增食欲素、P物质、去甲肾上腺素和乙酰胆碱在与延髓5-羟色胺系统相互作用中的作用；5)建立延髓5-羟色胺系统的组织和连通性，延髓5-羟色胺系统是由多个效应神经元介导的多种稳态功能的“集成者”；6)抑制(“沉默”)分子定义的5-羟色胺和GABA神经元亚群，并确定其在活体小鼠中的生理后果。在拟议的第三个周期中，我们将利用多学科方法测试凌驾性假说，其中人、动物、组织切片、细胞培养和发育数据被整合在一起，从而从细胞到系统水平相互告知和扩展以确定小岛屿发展中国家的发病机制。 项目1：小岛屿发展中国家脑内的神经化学病理学 (Kinney，Hannah，M.D.，第163-206页) 描述：项目1在上一个周期中的主要发现是延髓5-羟色胺(5-HT)系统的多种异常与小岛屿发展中国家有关。我们现在设想SIDS是一个复杂而不同的过程，除了5-羟色胺，还涉及多种递质，多种应激源同时作用，以及包括慢性缺氧和男性在内的多种遗传和环境因素，加剧了脑干缺陷。本研究的具体目的是：1)研究小岛屿发展中国家延髓内γ-氨基丁酸(GABA)的神经化学解剖。我们将与年龄调整后的对照组比较，测定SDS患者GABA神经元的数量和密度、与GABA共定位的5-羟色胺神经元的百分比、GABAA受体结合以及GABAA受体亚单位的细胞定位。2)测定SIDS患者延髓内SP阳性神经元和NK1受体的神经化学解剖。我们将与年龄调整的对照组比较，确定SDS病例中SP神经元的数量和密度、共定位SP的5-羟色胺神经元的百分比、SP结合和NK1的细胞定位。我们还将确定具有5-HT1A和推定的GABAA受体结合异常的SID病例是否与那些具有SP结合异常的病例相同。3)探讨雌激素和睾酮在小儿麻痹症骨髓病理中的作用。我们将测试假设：与年龄调整后的对照组相比，小岛屿发展中国家患者(男性和女性)延髓5-羟色胺系统和/或其投射部位的雄激素受体结合增加；在相同的小岛屿发展中国家中，高血清睾酮水平与高雄激素结合相关；血清睾酮水平高的男性小岛屿发展中国家的5-HT1a受体结合低于血清睾酮水平低的婴儿和对照组。4)探讨慢性间歇性低氧在小儿麻痹症髓质病理中的作用，以及5-羟色胺介导的可塑性缺陷在低氧反应中的作用。我们将检验这一假设，即与缺氧性病例相比，SIDS舌下核内的缺氧性反应减少，这反映在缺氧性标志物的减少上，例如促红细胞生成素。这一假说是基于这样一种观点，即低氧病例具有对低氧反应的“正常”能力，而小岛屿发展中国家则具有受损的能力。然后，我们将测试5-羟色胺介导的间歇性低氧可塑性(BDNF，TrkB受体)的标记物在SDS患者中比低氧患者舌下神经核中减少的假设。这一发现表明，由于5-羟色胺中缝相关的异常和长期促进功能受损，小岛屿发展中国家的婴儿无法适应间歇性低氧。拟议的研究建立在我们实验室20年来积累的独特数据库基础上出现的小岛屿发展中国家复杂脑干表型的图景。

DESCRIPTION (provided by applicant): Despite the success of the Back-to-Sleep campaign, the sudden infant death syndrome (SIDS) remains the leading cause of postneonatal infant mortality in the United States today. The major discovery of this program project in the last cycle was that multiple developmental abnormalities in the medullary serotonergic (5-HT) system are associated with SIDS. These human findings in Project 1 have lead to the establishment of a critical role for the medullary 5-HT system in the state-related regulation of multiple homeostatic functions in animal models in Projects 2-4. Additionally, they have lead to establishment of the developmental profile at the molecular level of the brainstem 5-HT system in Project 5. These discoveries have lead to the following over-riding hypothesis for the proposed third cycle: an important subset of SIDS is due to a developmental disorder of the medullary 5-HT system and related neuromodulator systems that are incurred prenatally, but which exerts its effects postnatally- during the first 6 months of life when the newborn, in transitioning to extrauterine life, undergoes maturation of circuitry for maintaining independent homeostasis and is at the greatest risk for SIDS. This disorder impairs protective homeostatic responses to potentially life-threatening, but often occurring, stressors during infant sleep that lead in turn to homeostatic derangements (hypoxia, hypercarbia), each potentially non-lethal in themselves, but which in combination precipitate death. Our objectives are: 1) To define the role of multiple transmitters/modulators in the neurochemical medullary pathology in SIDS infants; 2) To determine in rodent models the effect of homeostatic stressors-alone and in combination-upon autonomic and respiratory function during different sleep states, in males and females, and at different ages; 3) To determine the role of chronic intermittent hypoxia in the potentiation of the brainstem pathology in SIDS; 4) To determine the role of y-aminobutyric acid (GABA), orexin, substance P, norepinephrine, and acetylcholine in interacting with the medullary 5-HT system in homeostatic regulation in animal models; 5) To establish the organization and connectivity of the medullary 5-HT system-the "integrator" of diverse homeostatic functions mediated by multiple effector neurons; 6) To inhibit ("silence") molecularly defined subsets of 5-HT and GABA neurons and determine the physiological consequences in the living mouse. In the proposed third cycle, we will test the over-riding hypothesis utilizing a multidisciplinary approach in which human, animal, tissue slice, cell culture, and developmental data are integrated together, thereby informing and expanding upon each other towards establishing the pathogenesis of SIDS from the cellular to systems level. PROJECT 1: NEUROCHEMICAL PATHOLOGY IN SIDS BRAINSTEMS (Kinney, Hannah, M.D., pp 163-206) DESCRIPTION: The major discovery of Project 1 in the last cycle was that multiple abnormalities in the medullary serotonergic (5-HT) system are associated with SIDS. We now envision SIDS as a complex and heterogeneous process which involves multiple transmitters in addition to 5-HT, multiple stressors acting simultaneously, and multiple genetic and environmental factors, including chronic hypoxia and male gender, augmenting the brainstem defects. Our Specific Aims are: 1) To determine the neurochemical anatomy of Y-aminobutyric acid (GABA) in the medulla in SIDS cases. We will determine the number and density of GABA neurons, percent of 5-HT neurons that co-localize with GABA, GABAA receptor binding, and cellular localization of GABAA receptor subunits in SIDS cases compared with controls adjusted for age. 2) To determine the neurochemical anatomy of SP-expressing neurons and NK1 receptors in the medulla in SIDS cases. We will determine the number and density of SP neurons, the percent of 5-HT neurons that co-localize SP, SP binding, and cellular localization of NK1 in SIDS cases compared to controls adjusted for age. We will also determine if the SIDS cases with 5-HT1A and putative GABAA receptor binding abnormalities are the same as those with SP binding abnormalities. 3) To determine the role of estrogen and testosterone in the medullary pathology of SIDS. We will test the hypotheses that: androgen receptor binding is elevated in SIDS cases (male and female) in the medullary 5-HT system and/or its projection sites compared to controls adjusted for age; high serum testosterone levels correlate with high androgen binding in the same SIDS cases; and male SIDS cases with high serum testosterone levels have lower 5-HT1A receptor binding than SIDS infants with low serum testosterone levels and controls. 4) To determine the role of chronic intermittent hypoxia in the medullary pathology in SIDS and the role of compromised responses to hypoxia due to a defect in 5-HTmediated plasticity. We will test the hypothesis that SIDS cases show a reduced hypoxic response in the hypoglossal nucleus compared to hypoxic cases, as reflected in reduced hypoxic markers, e.g., erythropoietin. This hypothesis is based on the idea that hypoxic cases are equipped with a "normal" ability to respond to hypoxia, whereas the SIDS cases have an impaired ability. We will then test the hypothesis that markers of 5-HT-mediated plasticity to intermittent hypoxia (BDNF, TrkB receptors) are reduced in SIDS cases compared to hypoxic cases in the hypoglossal nucleus. This finding would suggest an inability of the SIDS infants to adapt to intermittent hypoxia due to 5-HT raphe-related abnormalities and impaired long-term facilitation. The proposed studies build upon an emerging picture of a complex brainstem phenotype in SIDS based upon a unique database accrued over 20 years in our laboratory.