The spa transgenic mouse displays spasticity and hypertonia that develops during the early postnatal period, with motor impairments that are remarkably similar to symptoms of human cerebral palsy. Previously, we observed that spa mice have fewer phrenic motor neurons innervating the diaphragm muscle (DIAm). We hypothesize that spa mice exhibit increased susceptibility to neuromuscular transmission failure (NMTF) due to an expanded innervation ratio. We retrogradely-labeled phrenic motor neurons with rhodamine and imaged them in horizontal sections (70 µm) using confocal microscopy. Phrenic nerve-DIAm strip preparations from wildtype and spa mice were stretched to optimal length, and force was evoked by phrenic nerve stimulation at 10, 40 or 75 Hz in 330 ms duration trains repeated each s (33% duty cycle) across a 120 s period. To assess NMTF, force evoked by phrenic nerve stimulation was compared to force evoked by direct DIAm stimulation superimposed every 15 s. Total DIAm fiber number was estimated in hematoxylin and eosin stained strips. Compared to wildtype, spa mice had over two-fold greater NMTF during the first stimulus train that persisted throughout the 120 s period of repetitive activation. In both wildtype and spa mice, NMTF was stimulation-frequency dependent. There was no difference in neuromuscular junction morphology or the total number of DIAm fibers between wildtype and spa mice, however there was an increase innervation ratio (39%) in spa mice. We conclude that early-onset developmental neuromotor disorders impair the efficacy of DIAm neuromuscular transmission, likely to contribute to respiratory complications.

中文翻译：

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早发性神经运动障碍小鼠模型的隔膜神经肌肉传递失败

spa 转基因小鼠表现出产后早期出现的痉挛和肌张力亢进，以及与人类脑瘫症状非常相似的运动障碍。以前，我们观察到 spa 小鼠支配膈肌 (DIAm) 的膈运动神经元较少。我们假设 spa 小鼠由于神经支配比例扩大而表现出对神经肌肉传递失败 (NMTF) 的易感性增加。我们用罗丹明逆行标记膈运动神经元，并使用共聚焦显微镜在水平切片 (70 µm) 中对它们进行成像。将来自野生型和 spa 小鼠的膈神经-DIAm 条带制剂拉伸至最佳长度，并在 10、40 或 75 赫兹下以 10、40 或 75 赫兹的频率刺激膈神经，在 330 毫秒的持续时间列车中，在 120 秒内重复每个秒（33% 占空比）时期。为了评估 NMTF，将膈神经刺激引起的力与每 15 秒叠加的直接 DIAm 刺激引起的力进行比较。在苏木精和曙红染色条中估计总 DIAm 纤维数。与野生型相比，在整个 120 秒的重复激活期间持续的第一次刺激训练中，spa 小鼠的 NMTF 高出两倍以上。在野生型和 spa 小鼠中，NMTF 都依赖于刺激频率。野生型和 spa 小鼠的神经肌肉接头形态或 DIAm 纤维总数没有差异，但 spa 小鼠的神经支配率增加 (39%)。我们得出结论，早发性发育性神经运动障碍会损害 DIAm 神经肌肉传递的功效，可能导致呼吸系统并发症。