Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota.
School of Biomedical Sciences, The University of Queensland, Brisbane, Australia.
J Appl Physiol (1985). 2021 Mar 1;130(3):708-720. doi: 10.1152/japplphysiol.00864.2020. Epub 2020 Dec 31.
The 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 mice have fewer phrenic motor neurons innervating the diaphragm muscle (DIAm). We hypothesize that 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 wild type and 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 second (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 wild type, mice had over twofold greater NMTF during the first stimulus train that persisted throughout the 120 s period of repetitive activation. In both wild type and mice, NMTF was stimulation-frequency dependent. There was no difference in neuromuscular junction morphology or the total number of DIAm fibers between wild type and mice, however, there was an increase innervation ratio (39%) in mice. We conclude that early-onset developmental neuromotor disorders impair the efficacy of DIAm neuromuscular transmission, likely to contribute to respiratory complications. Individuals with motor control deficits, including cerebral palsy (CP) often have respiratory impairments. Glycine-receptor mutant mice have early-onset hypertonia, and limb motor impairments, similar to individuals with CP. We hypothesized that in the diaphragm of mice, disruption of glycinergic inputs to MNs would result in increased phrenic-DIAm neuromuscular transmission failure. Pathophysiologic abnormalities in neuromuscular transmission may contribute to respiratory dysfunction in conditions where early developmental MN loss or motor control deficits are apparent.
该转基因小鼠表现出痉挛和张力亢进，这种情况在出生后早期发展，运动障碍与人类脑瘫的症状非常相似。以前，我们观察到 小鼠膈神经支配的膈肌（DIAm）运动神经元较少。我们假设 小鼠由于扩大的神经支配比例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神经运动神经元，并使用共聚焦显微镜在水平切片（70μm）中对其进行成像。来自野生型和 小鼠的膈神经-DIAm 条带制剂被拉伸到最佳长度，通过膈神经刺激在 10、40 或 75Hz 的 330ms 持续时间的列车中以每秒一次（33%占空比）重复 120 秒，以评估 NMTF，膈神经刺激引起的力与直接 DIAm 刺激引起的力进行比较，每隔 15s 叠加一次。在苏木精和伊红染色的条带中估计总 DIAm 纤维数。与野生型相比， 小鼠在前一个刺激列车期间的 NMTF 增加了两倍以上，这种情况持续到重复激活的 120 秒期间。在野生型和 小鼠中，NMTF 均与刺激频率相关。野生型和 小鼠之间的神经肌肉接头形态或 DIAm 纤维总数没有差异，但是 小鼠的神经支配比例增加了（39%）。我们得出结论，早期发病的神经运动障碍会损害 DIAm 神经肌肉传递的效率，可能导致呼吸并发症。运动控制缺陷的个体，包括脑瘫（CP），通常存在呼吸障碍。甘氨酸受体突变 小鼠具有早发性张力亢进和肢体运动障碍，与 CP 患者相似。我们假设在 小鼠的膈肌中，甘氨酸能输入到 MN 的中断会导致膈神经-DIAm 神经肌肉传递失败增加。神经肌肉传递的病理生理异常可能导致在早期发育 MN 丢失或运动控制缺陷明显的情况下出现呼吸功能障碍。
