DIAPHRAGM NEUROMUSCULAR TRANSMISSION: HYPOXIA & MATURITY

呼吸衰竭是新生儿期发病率的主要原因。来自我们和其他研究人员的证据表明，在这个年龄段，横隔膜疲劳是导致这种失败的原因，而神经肌肉传递(NMT)是失败的重要部位。根据我们实验室最近的数据，NMT失败的可能机制是神经递质不足。虽然已知钙在递质释放中起关键作用，但对这一过程的成熟和发育知之甚少。此外，在这个年龄段，与呼吸衰竭相关的缺氧是如何调节NMT的，我们知之甚少。因此，我们假设：1)在运动神经末梢，NMT失败是继发于突触前机制的。由于突触前神经末梢中特定亚型钙通道的结构和/或功能不成熟，CA2在NMT衰竭的发生发展中起着重要作用。这将在分离的大鼠横隔膜上进行测试：a)使用电生理学技术在钙通道亚型阻滞剂存在的情况下评估递质释放；以及b)使用免疫细胞化学和分子技术从形态上评估钙通道亚型。2)慢性低氧延缓NM连接的成熟。这与突触功能成熟延迟和突触效能降低有关。这将通过比较：a)形态；b)力量反应；c)动作电位故障；d)量子含量和安全系数；以及e)钙通道在出生后第一个月的几个时间点控制产仔大鼠。我们相信，这些研究将更好地了解新生儿横隔膜疲劳和呼吸衰竭的机制。

Respiratory failure is a major cause of morbidity in the newborn period. Evidence from our work and that of others suggests that in this age group diaphragmatic fatigue contributes to this failure, and that neuromuscular transmission (NMT) is an important site of failure. Based on recent data from our laboratory the probable mechanism underlying NMT failure is inadequate neurotransmitter. Although calcium is known to play a pivotal in transmitter release, little is known regarding the maturation of this process with development. Also, little is known regarding how the hypoxia that is associated with respiratory failure modulates NMT in this age group. Hence we hypothesize that: 1) NMT failure is secondary to presynaptic mechanisms at the motor nerve terminal. Ca2+ plays an important role in the development of NMT failure because of structural and/or functional immaturity of specific subtypes of Ca2+ channels in the presynaptic nerve terminal. This will be tested in the isolated rat diaphragm a) using electrophysiological techniques to assess transmitter release in the presence of blockers of Ca2+ channel subtypes; and b) morphologically assessing Ca2+ channel subtypes using immunocytochemistry and molecular techniques. 2) Chronic hypoxia delays the maturation of the NM junction. This is associated with delayed functional maturity of the synapse and decreased synaptic efficacy. This will be tested by comparing the: a) morphology; b) force response; c) action potentials failures; d) quantal content and safety factor; and e) Ca2+ channels of diaphragms of rats raised in chronic hypoxia to control littermates at several time points during the first postnatal month. We believe that these studies will provide a better understanding of the mechanisms underlying diaphragmatic fatigue and respiratory failure in the newborn.