Komuro A, Morimoto T, Iwata K, Inoue T, Masuda Y, Kato T, Hidaka O
Department of Oral Physiology, Graduate School of Dentistry, Osaka University, Osaka 565-0871, Japan.
J Neurophysiol. 2001 Dec;86(6):2834-44. doi: 10.1152/jn.2001.86.6.2834.
When a thin plastic test strip of various hardness is placed between the upper and lower teeth during rhythmical jaw movements induced by electrical stimulation of the cortical masticatory area (CMA) in anesthetized rabbits, electromyographic (EMG) activity of the masseter muscle is facilitated in a hardness-dependent manner. This facilitatory masseteric response (FMR) often occurred prior to contact of the teeth to the strip, and thus preceded the onset of the masticatory force. Since this finding suggests involvement of a feed-forward mechanism in the induction of the FMR, the temporal relationship between the onset of the FMR and that of the masticatory force was analyzed in five sequential masticatory cycles after application of the strip. The FMR was found to precede the onset of masticatory force from the second masticatory cycle after application of the strip, but never did in the first cycle. This finding supports the concept of a feed-forward control mechanism that modulates FMR timing. Furthermore, the FMR preceding the force onset disappeared after making a lesion of the mesencephalic trigeminal nucleus (MesV) where the ganglion cells of the muscle spindle afferents from the jaw-closing muscles are located. In contrast, no such change occurred after blocking periodontal afferents by transection of both the maxillary and the inferior alveolar nerves. The putative feed-forward control of the FMR is therefore dependent mainly on sensory inputs from the muscle spindles, but little on those from the periodontal receptors, if any. We further examined the involvement of the CMA with the putative feed-forward control of the FMR via the transcortical loop. For this purpose, rhythmical jaw movements were induced by stimulation of the pyramidal tract. No significant change in the timing of the FMR occurred after the CMA ablation, which strongly suggests that the CMA is not involved in the putative feed-forward control of the FMR. The FMR was also noted to increase significantly in a hardness-dependent manner even after the MesV lesion, although the rate of increment decreased significantly. Contribution of muscle spindles and periodontal receptors to the hardness-dependent change of the FMR is discussed.
在对麻醉的兔子的皮质咀嚼区（CMA）进行电刺激诱导的节律性下颌运动期间，当将各种硬度的薄塑料测试条置于上下牙齿之间时，咬肌的肌电图（EMG）活动以硬度依赖的方式得到促进。这种促进性咬肌反应（FMR）通常在牙齿接触测试条之前发生，因此在咀嚼力开始之前出现。由于这一发现表明在前馈机制参与了FMR的诱导，因此在放置测试条后的五个连续咀嚼周期中，分析了FMR开始与咀嚼力开始之间的时间关系。发现FMR在放置测试条后的第二个咀嚼周期开始先于咀嚼力开始，但在第一个周期中从未出现这种情况。这一发现支持了调节FMR时间的前馈控制机制的概念。此外，在位于咀嚼肌的肌梭传入神经节细胞所在的中脑三叉神经核（MesV）损伤后，力开始前的FMR消失。相比之下，在切断上颌神经和下牙槽神经以阻断牙周传入神经后，没有发生这种变化。因此，FMR的假定前馈控制主要依赖于来自肌梭的感觉输入，而很少依赖于来自牙周感受器的感觉输入（如果有的话）。我们进一步通过经皮质环路研究了CMA与FMR假定前馈控制的关系。为此，通过刺激锥体束诱导节律性下颌运动。在CMA切除后，FMR的时间没有发生显著变化，这强烈表明CMA不参与FMR的假定前馈控制。即使在MesV损伤后，FMR也以硬度依赖的方式显著增加，尽管增加率显著降低。讨论了肌梭和牙周感受器对FMR硬度依赖性变化的贡献。
