Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; Department of Special Needs Dentistry, Division of Oral Rehabilitation Medicine, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, Japan.
Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
Brain Res. 2022 Feb 15;1777:147753. doi: 10.1016/j.brainres.2021.147753. Epub 2021 Dec 13.
Trigeminal motoneurons (MNs) innervating the jaw-closing and jaw-opening muscles receive numerous inhibitory synaptic inputs from GABAergic and glycinergic neurons, which are essential for oromotor functions, such as the orofacial reflex, suckling, and mastication. The properties of the GABAergic and glycinergic inputs of these MNs undergo developmental alterations during the period in which their feeding behavior proceeds from suckling to mastication; however, the detailed characteristics of the developmental patterns of GABAergic and glycinergic transmission in these neurons remain to be elucidated. This study was conducted to investigate developmental changes in miniature inhibitory postsynaptic currents (mIPSCs) in masseter (jaw-closing) and digastric (jaw-opening) MNs using brainstem slice preparations obtained from Wistar rats on postnatal day (P)2-5, P9-12, and P14-17. The frequency and amplitude of glycinergic mIPSCs substantially increased with age in both the masseter and digastric MNs. The rise time and decay time of glycinergic mIPSCs in both MNs decreased during development. In contrast, the frequency of GABAergic components in masseter MNs was higher at P2-5 than at P14-17, whereas that in the digastric MNs remained unchanged throughout the postnatal period. The proportion of currents mediated by GABA-glycine co-transmission was higher at P2-5, and then it decreased with age in both MNs. These results suggest that characteristics related to the development of inhibitory synaptic inputs differ between jaw-closing and jaw-opening MNs and between GABAergic and glycinergic currents. These distinct developmental characteristics may contribute to the development of feeding behaviors.
三叉运动神经元（MNs）支配闭口和开口肌肉，它们接受来自 GABA 能和甘氨酸能神经元的大量抑制性突触输入，这些神经元对于口运动功能，如口面部反射、吸吮和咀嚼，是必不可少的。在这些 MNs 的摄食行为从吸吮转变为咀嚼的过程中，其 GABA 能和甘氨酸能输入的特性发生了发育变化；然而，这些神经元中 GABA 能和甘氨酸能传递的发育模式的详细特征仍有待阐明。本研究使用出生后第 2-5 天、第 9-12 天和第 14-17 天的 Wistar 大鼠脑干切片制备物，研究了咀嚼肌（闭口）和二腹肌（开口）MNs 中小型抑制性突触后电流（mIPSCs）的发育变化。在咀嚼肌和二腹肌 MNs 中，甘氨酸能 mIPSCs 的频率和幅度随年龄的增长而显著增加。甘氨酸能 mIPSCs 在这两种 MNs 中的上升时间和衰减时间在发育过程中减小。相比之下，在出生后第 2-5 天，咀嚼肌 MNs 中 GABA 能成分的频率高于第 14-17 天，而二腹肌 MNs 中的频率在整个出生后期间保持不变。在咀嚼肌和二腹肌 MNs 中，由 GABA-甘氨酸共传递介导的电流比例在出生后第 2-5 天较高，然后随着年龄的增长而降低。这些结果表明，与抑制性突触输入的发育相关的特征在闭口和开口 MNs 之间以及 GABA 能和甘氨酸能电流之间存在差异。这些不同的发育特征可能有助于摄食行为的发展。
