Park Sook Kyung, Hong Jae Hyun, Jung Jae Kwang, Ko Hyoung-Gon, Bae Yong Chul
Department of Anatomy and Neurobiology, Kyungpook National University, Daegu 41940, Korea.
Department of Oral Medicine, School of Dentistry, Kyungpook National University, Daegu 41940, Korea.
Exp Neurobiol. 2019 Aug 31;28(4):451-457. doi: 10.5607/en.2019.28.4.451.
Currently, compared to jaw-closing (JC) α-motoneurons, the information on the distribution and morphology of glutamatergic synapses on the jaw-closing (JC) γ-motoneurons, which may help elucidate the mechanism of isometric contraction of the JC muscle, is very limited. This study investigated the distribution and ultrastructural features of vesicular glutamate transporter 1 (VGLUT1)- and VGLUT2-immunopositive (+) axon terminals (boutons) on JC γ-motoneurons by retrograde tracing with horseradish peroxidase, electron microscopic immunocytochemistry, and quantitative analysis. About 35% of the boutons on identified JC γ-motoneurons were VGLUT+, and of those, 99% were VGLUT2+. The fraction of VGLUT1+ boutons of all boutons and the percentage of membrane of JC γ-motoneurons covered by these boutons were significantly lower than those for the JC α-motoneurons, revealed in our previous work. The bouton volume, mitochondrial volume, and active zone area of the VGLUT2+ boutons on the JC γ-motoneurons were uniformly small. These findings suggest that the JC γ-motoneurons, in contrast to the JC α-motoneurons, receive generally weak glutamatergic synaptic input almost exclusively from VGLUT2+ premotoneurons that form direct synapse with motoneurons.
目前，与闭口（JC）α运动神经元相比，关于闭口（JC）γ运动神经元上谷氨酸能突触的分布和形态的信息非常有限，而这些信息可能有助于阐明JC肌肉等长收缩的机制。本研究通过辣根过氧化物酶逆行追踪、电子显微镜免疫细胞化学和定量分析，研究了JCγ运动神经元上囊泡谷氨酸转运体1（VGLUT1）和VGLUT2免疫阳性（+）轴突终末（终扣）的分布和超微结构特征。在已鉴定的JCγ运动神经元上，约35%的终扣为VGLUT阳性，其中99%为VGLUT2阳性。所有终扣中VGLUT1阳性终扣的比例以及这些终扣覆盖的JCγ运动神经元膜的百分比，均显著低于我们之前工作中所揭示的JCα运动神经元的相应比例。JCγ运动神经元上VGLUT2阳性终扣的终扣体积、线粒体体积和活性区面积均较小。这些发现表明，与JCα运动神经元相比，JCγ运动神经元通常仅从与运动神经元形成直接突触的VGLUT2阳性运动前神经元接收较弱的谷氨酸能突触输入。
