title: Ultrastructural analysis of glutamate-immunopositive synapses onto the rat jaw-closing motoneurons during postnatal development.
abstract: The excitatory synapses on the jaw-closing (JC) motoneurons mediate the neuronal input that ensures smooth and rhythmic movements of the jaw. Recently, we have shown that the neurotransmitter phenotype of the inhibitory boutons onto JC motoneurons shifts from GABA to glycine, and new inhibitory synapses onto JC motoneurons are continuously formed during postnatal development (Paik et al. [2007] J. Comp. Neurol. 503:779–789). To test whether the developmental pattern of the excitatory synapses onto JC motoneurons differs from that of the inhibitory synapses, we studied the distribution of glutamate-immunopositive boutons onto the rat JC motoneurons during postnatal development by using a combination of retrograde labeling with horseradish peroxidase (HRP), postembedding immunogold staining, and quantitative ultrastructural analysis. The analysis of 175, 281, and 465 boutons contacting somata of JC motoneurons at postnatal days P2, P11, and P31, respectively, revealed that the number of glutamate-immunopositive (Glut(+)) boutons increased by 2.6 times from P2 to P11 and showed no significant change after that, whereas the length of apposition of these boutons increased continuously from P2 to P31, suggesting that the time course for the development of Glut(+) boutons differed from that for Glut(-) boutons, most of which were immunopositive for GABA and/or glycine. Our findings indicate that excitatory and inhibitory synapses onto JC motoneurons exhibit distinctly different developmental patterns that may be closely related to the maturation of the masticatory system.
authors.affiliation: Department of Oral Anatomy and Neurobiology, BK21, School of Dentistry, Kyungpook National University, Jung-Gu, Daegu, South Korea.
authors.forename: Sang Kyoo
authors.initials: SK
authors.lastname: Paik
authors.forename: Sook Kyung
authors.initials: SK
authors.lastname: Park
authors.forename: Jong Kil
authors.initials: JK
authors.lastname: Jin
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Bae
authors.forename: Su Jung
authors.initials: SJ
authors.lastname: Choi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yoshida
authors.forename: Dong Kuk
authors.initials: DK
authors.lastname: Ahn
authors.forename: Yong Chul
authors.initials: YC
authors.lastname: Bae
mesh_terms: D000818:Animals; D018698:Glutamic Acid / Q000378:metabolism; D007150:Immunohistochemistry; D007568:Jaw / Q000294:innervation* / Q000648:ultrastructure; D008297:Male; D046529:Microscopy, Electron, Transmission; D009046:Motor Neurons / Q000378:metabolism / Q000648:ultrastructure*; D055495:Neurogenesis; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014278:Trigeminal Nuclei / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D018698:Glutamic Acid