Exp Neurobiol. 2019; 28(4): 451-457
Published online August 31, 2019
© The Korean Society for Brain and Neural Sciences
Sook Kyung Park1†, Jae Hyun Hong1†, Jae Kwang Jung2, Hyoung-Gon Ko1 and Yong Chul Bae1*
Departments of 1Anatomy and Neurobiology, 2Oral Medicine, School of Dentistry, Kyungpook National University, Daegu 41940, Korea
Correspondence to: TEL: 82-53-660-6860, FAX: 82-53-426-7731
†S.K. Park and J.H. Hong contributed equally to this work.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License
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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.