Mechanisms of Hypoxia-Mediated Disturbances in Cerebral Maturation in a Fetal Ovine Model of Maternal Sleep Apnea

项目摘要 虽然睡眠呼吸紊乱引起的睡眠呼吸暂停通常发生在怀孕期间，但 母亲短暂反复间歇性低氧(IHx)对胎儿脑发育的累积影响 是未知的。我们开发了一种新的临床相关的母体IHx模型，该模型可重复性地导致 妊娠晚期早期胎儿全身性IHx。胎儿的海马体似乎对 母体IHx，慢性扰乱神经元活动和学习记忆的细胞机制。我们的 最重要的假设是，母体IHx在全球范围内扰乱了胎儿的大脑发育，并导致持续性 出生后学习和记忆的变化。在目标1中，我们将首先使用近红外光谱来定义 宫内IHx对清醒胎儿脑组织低氧血症的影响接下来我们将确定 胎儿海马体对细胞死亡、炎症和白质损伤的易感性。我们还将确定 母体IHx对形成神经元树突和棘密度的成熟障碍的影响 行为上重要的神经回路，调节突触可塑性和神经传递 发展。补充电生理学研究将确定IHx对突触的功能影响 电刺激对海马神经元的传递、长时程增强和内源性兴奋性的影响 潜能；这些都是体内调节学习和记忆的关键细胞机制。AIM 2将聘用 补充先进的MRI和形态计量学方法分析相对易感性 与胎儿IHx相关的海马区，这可能通过定义全球 母体IHx对最佳神经发育和回路形成所需的关键脑区的影响。我们 将确定胎儿大脑生长和成熟、细胞死亡、炎症等区域性障碍的频谱 并提供了髓鞘形成差异和胎儿脑体积差异的定量分析。在《目标3》中， 机械性胎儿海马区研究将检验增强海马区突触传递的假说 在CA3-CA1突触将逆转母体IHx介导的胎儿海马突触可塑性障碍， 这是学习和记忆细胞机制发育成熟的基础。我们将决定 在3.1中，干扰对AMPA和NMDA受体亚单位组成和表达水平的影响 谷氨酸能突触传递和长时程增强的障碍。在3.2中，我们将确定 变构AMPA受体激动剂(Ampakine)增强突触传递和体外可塑性。在3.3版本中， 我们将进行开创性的神经行为研究，以确定胎儿海马区突触是否中断 可塑性导致幼年羔羊持续的海马区学习和记忆障碍。我们的长期合作 目的是确定母体IHx干扰胎儿大脑成熟和发育的机制。 减少母体IHx对大脑发育的妊娠相关并发症的策略，这可能 改善学习和记忆。

Project Summary Although sleep apnea arising from sleep-disordered breathing commonly occurs during pregnancy, the cumulative impact of brief repetitive episodes of maternal intermittent hypoxia (IHx) on fetal brain development is unknown. We have developed a novel clinically relevant model of maternal IHx, which reproducibly results in fetal systemic IHx early in the third trimester. The fetal hippocampus appears to be particularly sensitive to maternal IHx, which chronically disrupts neuronal activity and cellular mechanisms of learning and memory. Our over-riding hypothesis is that maternal IHx globally disrupts fetal cerebral development and results in persistent changes in postnatal learning and memory. In aim 1, we will first employ near infrared spectroscopy to define cerebral tissue hypoxemia in awake fetuses subjected to maternal IHx in utero. We will next determine the susceptibility of the fetal hippocampus to cell death, inflammation and white matter injury. We will also determine the impact of maternal IHx on disturbances in maturation of neuronal dendrites and spine density, which shape behaviorally important neural circuits, which regulate synaptic plasticity and neurotransmission during development. Complementary electrophysiological studies will determine the functional effects of IHx on synaptic transmission, long-term synaptic potentiation (LTP) and intrinsic excitability of hippocampal neurons to fire action potentials; which are all key cellular mechanisms that mediate learning and memory in vivo. Aim 2 will employ complementary advanced MRI and morphometric approaches to analyze the relative susceptibility of hippocampal-related brain regions to fetal IHx, which could inform future clinical studies by defining the global impact of maternal IHx on key brain regions required for optimal neurodevelopment and circuit formation. We will determine the spectrum of regional disturbances in fetal brain growth and maturation, cell death, inflammation and myelination and provide a quantitative analysis of differences in fetal brain volume differences. In aim 3, mechanistic fetal hippocampal studies will test the hypothesis that enhancing hippocampal synaptic transmission at CA3-CA1 synapses will reverse maternal IHx-mediated disturbances in fetal hippocampal synaptic plasticity, which underlie the developmental maturation of cellular mechanisms of learning and memory. We will determine in 3.1 the contribution of disturbances in AMPA and NMDA receptor subunit composition and expression levels to disturbances in glutamatergic synaptic transmission and LTP. In 3.2, we will determine the efficacy of an allosteric AMPA receptor agonist (ampakine) to strengthen synaptic transmission and plasticity in vitro. In 3.3, We will undertake pioneering neurobehavioral studies to determine if disrupted fetal hippocampal synaptic plasticity results in persistent hippocampal learning and memory deficits in juvenile lambs. Our long-term objectives are to define mechanisms through which maternal IHx disrupts fetal cerebral maturation and develop strategies to mitigate pregnancy-associated complications of maternal IHx on brain development, which may improve learning and memory.