Functional Analysis of Rhythmic Jaw Movements Evoked by Electrical Stimulation of the Cortical Masticatory Area During Low Occlusal Loading in Growing Rats
Functional Analysis of Rhythmic Jaw Movements Evoked by Electrical Stimulation of the Cortical Masticatory Area During Low Occlusal Loading in Growing Rats
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DOI：
10.3389/fphys.2020.00034
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发表时间：
2020-01-31
影响因子：
4
通讯作者：
Ono, Takashi
中科院分区：
文献类型：
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作者：
Aung, Phyo Thura;Kato, Chiho;Ono, Takashi
虽然节律颚运动（RJMs）的成熟和相关的神经肌肉控制在调节口颌功能的发展中是必不可少的，但很少在动物中进行研究。先前的研究表明，生长期间的咬合功能障碍会改变咀嚼功能。然而，在发育过程中，在软性饮食喂养条件下，皮质诱导RJMs的模式知之甚少。本研究的目的是阐明低咬合负荷对生长大鼠皮质诱导RJMs模式和相关神经肌肉反应的影响。将64只2周龄雄性白化Wistar大鼠随机分为两组，分别饲喂正常饲粮（对照组）和软饲粮（实验组）。在5、7、9和11周龄时，记录右咬肌和前二腹肌的肌电图（EMG）活动，并在左皮质咀嚼区（CMA）的重复皮质内微刺激中记录RJMs中相应的运动学图像。两组大鼠在9周龄前均表现出开口大小和外侧偏移的增加。两组在5 ~ 7周龄间的垂直下颚运动速度无显著差异，在9 ~ 11周龄间随年龄增长而增加。与对照组相比，实验组的平均开口大小和垂直速度显著降低，且两组在各记录年龄的下颌运动周期模式和节奏相似。肌电图记录显示，在发病潜伏期、持续时间和峰对峰振幅方面，没有与年龄相关的显著差异。此外，我们发现实验组的发病潜伏期明显长于对照组，峰间振幅明显小于对照组，平均和中位数频率下降幅度明显大于对照组，而组间持续时间无显著差异。这些发现表明，婴儿期缺乏足够的咬合功能会阻碍RJMs模式的发展，并延迟CMA特异性刺激的神经肌肉反应。
The maturation of rhythmic jaw movements (RJMs) and related neuromuscular control has rarely been studied in animals, though this process is essential for regulating the development of stomatognathic functions. Previous studies have shown that occlusal hypofunction during growth alters masticatory performance. However, little is known about patterns of cortically-induced RJMs under conditions of soft-diet feeding during development. The aim of this study is to clarify the effect of low occlusal loading on the pattern of cortically induced RJMs and related neuromuscular responses in growing rats. Sixty-four 2-week-old male albino Wistar rats were randomly divided into two groups and fed on either a normal diet (control) or soft diet (experimental) soon after weaning. At 5, 7, 9, and 11 weeks of age, electromyographic (EMG) activity was recorded from the right masseter and anterior digastric muscles along with corresponding kinematic images in RJMs during repetitive intracortical microstimulation of the left cortical masticatory area (CMA). Rats in both groups showed an increase in gape size and lateral excursion until 9 weeks of age. The vertical jaw movement speed in both groups showed no significant difference between 5 and 7 weeks of age but increased with age from 9 to 11 weeks. Compared to the control group, the average gape size and vertical speed were significantly lower in the experimental group, and the pattern and rhythm of the jaw movement cycle were similar between both groups at each recording age. EMG recordings showed no age-related significant differences in onset latency, duration, and peak-to-peak amplitude. Moreover, we found significantly longer onset latency, smaller peak-to-peak amplitude, and greater drop-off mean and median frequencies in the experimental group than in the control group, while there was no significant difference in the duration between groups. These findings indicate that a lack of enough occlusal function in infancy impedes the development of patterns of RJMs and delays the neuromuscular response from specific stimulation of the CMA.