Localization and functional role of interneurons in the brainstem involved in chewing and swallowing

在清醒和麻醉的动物以及人类受试者中进行电生理学研究。在动物实验中，用咬肌、二腹肌和颏舌肌肌电记录脑干中间神经元的活动。电刺激下牙槽神经和上级喉神经分别诱发颌反射和吞咽反射，同时刺激咀嚼皮质区诱发虚拟咀嚼。记录中间神经元和/或肌肉活动以研究它们如何被外周/中枢刺激调制。记录中间神经元的活动非常困难，因为它们对呼吸非常敏感，呼吸也受到刺激的调节。因此，我们将目光转向输出系统，以了解其功能。在动物的慢性实验中，在咀嚼和吞咽过程中评价颌反射反应的变化。结果表明，咀嚼和吞咽时的反射都受到抑制，吞咽时的反射调制比咀嚼时的反射调制要温和。结果表明，对运动神经元的调制输入分别来自咀嚼中枢和吞咽中枢。另一方面，在人类中，在颏舌肌的EMG活动中研究了调制模式，颏舌肌是舌外肌之一，已知其关键功能是制作食物团并将其通过口咽输送到食管。舌的前部和后部以不同的方式受到外周输入的调制。它可能有助于完成摄入。

An electrophysiological study was performed in awake and anesthetized animals as well as human subjects. In animal experiments, interneuron activities in the brainstem were recorded with EMGs of masseter, digastric and genioglossus muscles. Electrical stimulation was applied in the inferior alveolar and superior laryngeal nerves to evoke the jaw reflex and swallowing reflex, respectively, while the cortical masticatory area was also stimulated to evoke the fictive mastication. Interneuron and/or muscle activity was recorded to investigate how they were modulated by the peripheral/central stimulation. It was very difficult to record interneuron activity because they were very sensitive to the respiration which was also modulated by the stimulation. We, therefore, moved our eyes to the output system to understand the function. In chronic experiments of animals, changes in jaw reflex responses were evaluated during chewing and swallowing. The results showed that the reflexes were suppressed not only during chewing but also during swallowing, and the modulation during swallowing was moderate as compared to that during chewing. The results suggest that the modulatory inputs to motoneurons exist from the chewing center and swallowing center independently. On the other hand, in humans, modulatory pattern was investigated in the EMG activity of the genioglossus muscle which was one of the extrinsic tongue muscles and was known to critically function as making the food bolus and transporting it through the oropharynx to the esophagus. the anterior and posterior portions of tongue were modulated by the peripheral inputs in a different manner. It may contribute to completion of ingestion.