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

描述（由申请人提供）：婴儿猝死综合征（SIDS）是美国新生儿死亡后最常见的原因，其机制尚不清楚，但在尸检研究中一直发现血清素系统异常。因此，确定血清素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SIDS。我们提出中缝核的血清素神经元是动脉二氧化碳的传感器，通过诱导觉醒、呼吸增加和其他旨在恢复pH/CO2稳态的变化来响应高碳酸血症。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受的缺陷可能导致对气道阻塞或睡眠期间再呼吸的正常通气反应丧失。我们现在计划用两种在血清素神经元发育上有缺陷的转基因小鼠来直接测试血清素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%的血清素神经元。我们的初步数据表明，雄性Pet1 KO小鼠在成年高碳酸血症通气反应方面存在缺陷。另一种小鼠系是在共表达Pet1的细胞中组织特异性敲除Lmx1 b。这些小鼠选择性地失去了99%的血清素神经元。他们活到成年，很少有异常。然而，它们在二氧化碳化学接受方面存在严重缺陷。我们将成年和新生小鼠暴露于高碳酸血症和低氧环境中，测量通气、心率、运动活动和脑电图。我们还将研究产前暴露于香烟烟雾对野生型和突变型小鼠的影响。然后，我们将使用灌注脑准备和脑切片来确定呼吸节律产生是否发生改变或呼吸网络对二氧化碳的反应是否降低。最后，我们将使用活体、灌注脑和脑切片制剂来确定血清素或促甲状腺素释放激素是否可以恢复成年Lmxlb条件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中的正常作用，并可能解释5 -羟色胺系统的缺陷如何导致在关键发育时期睡眠时死亡。这可能为SIDS与血清素系统缺陷之间的关联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.