Does neurotransmitter plasticity of para-serotonergic neurons augment autoresuscitation following perinatal stress and buffer SIDS risk?

项目摘要：一个强大的自动复苏反射（AR）是至关重要的新生儿从出生存活。的 过渡到独立呼吸和适应呼吸中断，呼吸暂停，这是常见的， 新生儿和婴儿需要协调的心肺反应以恢复。5-羟色胺（5- HT，血清素）和产生它的脑干中缝细胞，称为Pet 1神经元，组织和驱动 在新生动物和人类中成功的AR。不成功的AR被认为是导致 婴儿猝死综合征（SIDS），其中大脑5-HTergic系统的改变已被发现。 在约一半的人类SIDS病例中描述，包括不同形态的5-HT神经元数量增加 （更小，更简单，可能不成熟），自身受体5-HT 1A结合缺陷，以及5-HT 1A水平降低， HT和色氨酸羟化酶2（TPH 2，5-HT的限速生物合成酶）。我们提出 在小鼠中揭示这种SIDS脑5-HTergic表型的各个方面是如何在产前发育的。我们 最近的两项研究结果为这种方法提供了信息。首先，中缝核中的Pet 1+神经元表达高水平的5-HT， 已经鉴定了一些身份基因（例如Ddc、Vmat 2、Gata 3、Pet 1），它们的大小较小，具有适度水平的 自身受体5-HT 1A显著表达很少或不表达TPH 2和5-HT。我们称这些新细胞为帕拉-5- HTergic神经元，表明它们部分共享的分子表型，共享的位置和发育 出现5-HT神经元。第二个是发现神经递质转换，一种非规范的形式， 神经元对压力的可塑性。最近的数据支持其在塑造5-HTergic中的作用 神经元系统，其中应激源可以驱动一些5-HT旁神经元产生5-HT作为适应性神经元。 反应初步结果表明帕拉-HT神经元密集地起源于菱形节（r）4， 选择性地支配呼吸和唤醒中心，妊娠期暴露于间歇性缺氧 导致出生后TPH 2+细胞数量增加，5-HT水平尚不确定。我们建议 帕拉-羟色胺神经元是一个可塑的群体，当受到产前刺激时， 缺氧可使新生儿产生5-HT，作为支持AR的代偿机制。我们假设 为了应对产前缺氧这一SIDS的主要危险因素，帕拉-HT神经元自适应地 转化产生5-HT以纠正阻碍AR的5-HT能信号传导失衡， 换句话说，转型不充分在小岛屿发展中国家发挥着关键作用。我们将通过暴露 小鼠间歇性缺氧或常氧在怀孕期间，表征细胞和分子表型 和查询神经递质转化（目标1）;进一步，我们将确定急性激活的影响 或抑制这些小鼠中AR上的这些r4-帕拉-5-HT神经元（目的2），我们将检查表型 人SIDS和对照脑组织中的帕拉-5-HT神经元的标记物（目的3）。这部小说，功能上 定义，帕拉5-HT细胞类型和可塑性可能是高度相关的新生儿的生存能力。

Project Summary: A robust autoresuscitatory reflex (AR) is critical to newborn survival from birth. The transition to independent breathing and accommodation of breathing interruptions, apneas, that are common in neonates and infants, requires a coordinated cardiorespiratory response for recovery. 5-hydroxytryptamine (5- HT, serotonin) and the brainstem raphe cells that produce it, referred to as Pet1 neurons, organize and drive successful AR in newborn animals and humans. Unsuccessful AR is understood to be a major contributor to the sudden infant death syndrome (SIDS), where alterations in the brain 5-HTergic system have been described in ~half of human SIDS cases, including increased number of 5-HT neurons of differing morphology (smaller, simpler, perhaps immature), deficiencies in autoreceptor 5-HT1A binding, and decreased levels of 5- HT and tryptophan hydroxylase 2 (TPH2, the rate-limiting biosynthetic enzyme for 5-HT). We propose investigations to reveal in mice how aspects of this SIDS brain 5-HTergic phenotype develop prenatally. Our approach is informed by two recent findings. First, Pet1+ neurons in the raphe expressing high levels of 5-HT identity genes (e.g. Ddc, Vmat2, Gata3, Pet1) have been identified, smaller in size, with modest levels of autoreceptor 5-HT1A yet remarkably expressing little or no TPH2 and 5-HT. We call these novel cells para-5- HTergic neurons, signifying their partially shared molecular phenotype, shared location, and developmental emergence with 5-HT neurons. Second is the discovery of neurotransmitter switching, a noncanonical form of neuronal plasticity that occurs in response to stressors. Recent data support its role in shaping the 5-HTergic neuronal system, where stressors may drive some para-5-HT neurons to produce 5-HT as an adaptive response. Preliminary findings reveal that para-5-HT neurons derived from rhombomere (r) 4 densely and selectively innervate respiratory and arousal centers, and that gestational exposure to intermittent hypoxia results in an increased number of TPH2+ cells postnatally with as yet uncertain 5-HT levels. We propose that para-5-HT neurons are a pliant population that may be transformed when challenged prenatally by hypoxia to produce 5-HT in newborns as a compensatory mechanism to support AR. We hypothesize that in response to the major SIDS risk factor of prenatal hypoxia, certain para-5-HT neurons adaptively transform to produce 5-HT to rectify a 5-HTergic signaling imbalance that hinders the AR and, alternatively, that an insufficient transformation plays a critical role in SIDS. We will test this by exposing mice to intermittent hypoxia or normoxia during gestation, characterizing cellular and molecular phenotypes and querying neurotransmitter transformation (Aim 1); further, we will determine the effect of acute activation or inhibition of these r4-para-5-HT neurons on the AR in these mice (Aim 2), and we will examine phenotypic markers of para-5-HT neurons in human SIDS and control brain tissue (Aim 3). This novel, functionally defined, para-5-HT cell type and plasticity may be highly relevant to newborn viability.