Developmental defects in serotonin neurons and the response to O2 and CO2

描述(申请人提供)：婴儿猝死综合症(SID)是美国新生儿后死亡的最常见原因。其机制尚不清楚，但在尸检研究中一直发现血清素系统的异常。因此，明确5-羟色胺神经元在正常脑功能中的作用，这也是一个重要的科学目标，可能有助于理解SID。我们已经提出，中缝核团的5-羟色胺神经元是动脉二氧化碳的感受器，通过诱导觉醒、呼吸增加和其他旨在恢复pH/CO2动态平衡的变化来对高二氧化碳做出反应。这与小岛屿发展中国家的流行病学是一致的，因为二氧化碳化学接收的缺陷可能会导致对呼吸道阻塞或睡眠中重复呼吸的正常呼吸系统反应的丧失。我们现在计划使用两个基因改变的小鼠，在这些小鼠中，5-羟色胺神经元的发育存在缺陷，以直接测试5-羟色胺神经元是二氧化碳化学感受器的假设。有一种小鼠缺乏Pet1，并且只有正常数量的30%的5-羟色胺神经元。我们的初步数据表明，成年雄性Pet1KO小鼠在高碳酸血症的呼吸反应中存在缺陷。小鼠的另一个品系是在共表达Pet1的细胞中对Lmx1b进行组织特异性敲除。这些小鼠选择性地丧失了99%的5-羟色胺神经元。它们可以活到成年，几乎没有异常。然而，它们在二氧化碳化学接收方面存在严重缺陷。我们将使成年和新生小鼠暴露在高碳酸血症和低氧下，并测量通气量、心率、运动活动和脑电。我们还将研究出生前暴露在香烟烟雾中的野生型和突变小鼠的影响。然后，我们将使用灌流的脑准备和脑切片来确定是否存在呼吸节律生成的改变或呼吸网络对二氧化碳的反应减弱。最后，使用活体、灌流脑和脑切片准备，我们将确定5-羟色胺或促甲状腺激素释放激素是否可以恢复成年Lmxlb条件性基因敲除小鼠的正常呼吸。这些实验将有助于确定5-羟色胺神经元在控制呼吸、自主神经功能和觉醒方面的正常作用，并可能解释5-羟色胺系统缺陷如何导致在关键发育时期睡眠时死亡。这可能为SID与5-羟色胺系统缺陷之间的联系提供了一种特定的神经生物学机制。

DESCRIPTION (provided by applicant): Sudden infant death syndrome (SIDS) is the most common cause of post neonatal infant death in the U.S. The mechanisms are unknown, but abnormalities in the serotonin system have been consistently found in autopsy studies. Thus, defining the role of serotonin neurons in normal brain function, which is also an important scientific goal, may help to understand SIDS. We have proposed that serotonin neurons of the raphe nuclei are sensors of arterial carbon dioxide that respond to hypercapnia by inducing arousal, an increase in breathing, and other changes aimed at restoring pH/CO2 homeostasis. This is consistent with the epidemiology of SIDS, because a defect in CO2 chemoreception could lead to loss of the normal ventilatory response to airway obstruction or rebreathing during sleep. We now plan to use two lines of genetically altered mice in which there is a defect in development of serotonin neurons to directly test the hypothesis that serotonin neurons are CO2 chemoreceptors. One line of mouse lacks Pet1, and has only 30% of the normal number of serotonin neurons. Our preliminary data indicate that male Pet1 KO mice have a defect in the hypercapnic ventilatory response as adults. The other line of mouse is a tissue specific knockout of Lmx1 b in cells that co-express Pet1. These mice have a selective loss of >99% of serotonin neurons. They live to adulthood with relatively few abnormalities. However, they have a severe defect in CO2 chemoreception. We will expose adult and neonatal mice to hypercapnia and hypoxia, and measure ventilation, heart rate, motor activity and EEG. We will also examine the effect on wild-type and mutant mice of prenatal exposure to cigarette smoke. We will then use the perfused brain preparation and brain slices to determine whether there is an alteration of respiratory rhythm generation or decreased response of the respiratory network to CO2. Finally, using in vivo, perfused brain and brain slice preparations, we will determine whether serotonin or thyrotropin releasing hormone can restore normal breathing in adult Lmxlb conditional knockout mice. These experiments will help define the normal role of serotonin neurons in control of breathing, autonomic function and arousal, and may explain how a defect in the serotonin system could lead to death while sleeping during a critical developmental period. This may provide a specific neurobiological mechanism for the association between SIDS and defects in the serotonin system.