Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, 188-1, 2-Ga, Samdeok-Dong, Jung-Gu, Daegu, 700-412, Korea.
Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, Osaka, 565-0871, Japan.
Brain Struct Funct. 2021 Apr;226(3):889-900. doi: 10.1007/s00429-021-02216-9. Epub 2021 Jan 21.
Detailed information about the development of excitatory and inhibitory synapses on the genioglossal (GG) motoneuron may help to understand the mechanism of fine control of GG motoneuron firing and the coordinated tongue movement during postnatal development. For this, we investigated the development of γ-aminobutyric acid (GABA)-immunopositive (GABA +), glycine + (Gly +), and glutamate + (Glut +) axon terminals (boutons) on the somata of rat GG motoneurons at a postnatal day 2 (P2), P6 and P18 by retrograde labeling of GG motoneurons with horseradish peroxidase, electron microscopic postembedding immunogold staining with GABA, Gly, and Glut antisera, and quantitative analysis. The number of boutons per GG motoneuron somata and the mean length of bouton apposition, measures of bouton size and synaptic covering percentage, were significantly increased from P2/P6 to P18. The number and fraction of GABA + only boutons of all boutons decreased significantly, whereas those of Gly + only boutons increased significantly from P2/P6 to P18, suggesting developmental switch from GABAergic to glycinergic synaptic transmission. The fraction of mixed GABA +/Gly + boutons of all boutons was the highest among inhibitory bouton types throughout the postnatal development. The fractions of excitatory and inhibitory boutons of all boutons remained unchanged during postnatal development. These findings reveal a distinct developmental pattern of inhibitory synapses on the GG motoneurons different from that on spinal or trigeminal motoneurons, which may have an important role in the regulation of the precise and coordinated movements of the tongue during the maturation of the oral motor system.
详细了解舌下神经（GG）运动神经元上兴奋性和抑制性突触的发育情况，有助于理解 GG 运动神经元放电的精细控制机制和出生后发育过程中舌协调运动的机制。为此，我们通过辣根过氧化物酶逆行标记 GG 运动神经元，用 GABA、Gly 和 Glut 抗血清进行电镜后包埋免疫金染色，并进行定量分析，研究了 GABA 免疫阳性（GABA+）、甘氨酸+（Gly+）和谷氨酸+（Glut+）轴突末梢（终末）在出生后第 2 天（P2）、第 6 天（P6）和第 18 天（P18）大鼠 GG 运动神经元体上的发育情况。每个 GG 运动神经元体上的终末数和终末贴附的平均长度、终末大小和突触覆盖百分比的测量值均从 P2/P6 显著增加到 P18。GABA+ 终末的数量和比例显著减少，而 Gly+ 终末的数量和比例显著增加，提示从 GABA 能突触传递向 Gly 能突触传递的发育性转变。在整个出生后发育过程中，所有终末中混合 GABA+/Gly+ 终末的比例最高。兴奋性和抑制性终末的比例在出生后发育过程中保持不变。这些发现揭示了 GG 运动神经元上抑制性突触的发育模式与脊髓或三叉运动神经元上的不同，这可能在口腔运动系统成熟过程中对舌的精确和协调运动的调节具有重要作用。
