Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555 Japan.
Department of Perioperative Medicine, Division of Anesthesiology, Showa University School of Dentistry, 2-2-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, Japan.
Neuroscience. 2022 Jan 1;480:42-55. doi: 10.1016/j.neuroscience.2021.11.016. Epub 2021 Nov 12.
Motoneurons that innervate the jaw-closing and jaw-opening muscles play a critical role in oro-facial behaviors, including mastication, suckling, and swallowing. These motoneurons can alter their physiological properties through the postnatal period during which feeding behavior shifts from suckling to mastication; however, the functional synaptic properties of developmental changes in these neurons remain unknown. Thus, we explored the postnatal changes in glutamatergic synaptic transmission onto the motoneurons that innervate the jaw-closing and jaw-opening musculatures during early postnatal development in rats. We measured miniature excitatory postsynaptic currents (mEPSCs) mediated by non-NMDA receptors (non-NMDA mEPSCs) and NMDA receptors in the masseter and digastric motoneurons. The amplitude, frequency, and rise time of non-NMDA mEPSCs remained unchanged among postnatal day (P)2-5, P9-12, and P14-17 age groups in masseter motoneurons, whereas the decay time dramatically decreased with age. The properties of the NMDA mEPSCs were more predominant at P2-5 masseter motoneurons, followed by reduction as neurons matured. The decay time of NMDA mEPSCs of masseter motoneurons also shortened remarkably across development. Furthermore, the proportion of NMDA/non-NMDA EPSCs induced in response to the electrical stimulation of the supratrigeminal region was quite high in P2-5 masseter motoneurons, and then decreased toward P14-17. In contrast to masseter motoneurons, digastric motoneurons showed unchanged properties in non-NMDA and NMDA EPSCs throughout postnatal development. Our results suggest that the developmental patterns of non-NMDA and NMDA receptor-mediated inputs vary among jaw-closing and jaw-opening motoneurons, possibly related to distinct roles of respective motoneurons in postnatal development of feeding behavior.
支配闭口和开口肌肉的运动神经元在口面行为中发挥着关键作用，包括咀嚼、吸吮和吞咽。这些运动神经元可以通过出生后的时期改变其生理特性，在此期间，摄食行为从吸吮转变为咀嚼；然而，这些神经元发育过程中功能性突触特性仍不清楚。因此，我们在大鼠出生后早期发育过程中探索了支配闭口和开口肌肉的运动神经元中谷氨酸能突触传递的发育变化。我们测量了咀嚼肌和二腹肌运动神经元中非 NMDA 受体（非 NMDA mEPSC）和 NMDA 受体介导的微小兴奋性突触后电流（mEPSC）。在咀嚼肌运动神经元中，非 NMDA mEPSC 的幅度、频率和上升时间在出生后第 2-5 天（P2-5）、第 9-12 天（P9-12）和第 14-17 天（P14-17）年龄组之间保持不变，而衰减时间则随年龄显著下降。NMDA mEPSC 的特性在 P2-5 咀嚼肌运动神经元中更为突出，随后随着神经元成熟而减少。咀嚼肌运动神经元 NMDA mEPSC 的衰减时间在整个发育过程中也显著缩短。此外，电刺激三叉神经上区域诱导的 NMDA/非 NMDA EPSC 的比例在 P2-5 咀嚼肌运动神经元中相当高，然后在 P14-17 时下降。与咀嚼肌运动神经元相反，二腹肌运动神经元在整个出生后发育过程中表现出非 NMDA 和 NMDA EPSC 的不变特性。我们的结果表明，非 NMDA 和 NMDA 受体介导的输入在闭口和开口运动神经元中的发育模式不同，这可能与各自运动神经元在出生后摄食行为发育中的不同作用有关。
