title: γ-Aminobutyric acid-, glycine-, and glutamate-immunopositive boutons on mesencephalic trigeminal neurons that innervate jaw-closing muscle spindles in the rat: ultrastructure and development.
abstract: Unlike other primary sensory neurons, the neurons in the mesencephalic trigeminal nucleus (Vmes) receive most of their synaptic input onto their somata. Detailed description of the synaptic boutons onto Vmes neurons is crucial for understanding the synaptic input onto these neurons and their role in the motor control of masticatory muscles. For this, we investigated the distribution of γ-aminobutyric acid (GABA)-, glycine-, and glutamate-immunopositive (+) boutons on Vmes neurons and their ultrastructural parameters that relate to transmitter release: Vmes neurons that innervate masseteric muscle spindles were identified by labeling with horseradish peroxidase injected into the muscle, and immunogold staining and quantitative ultrastructural analysis of synapses onto these neurons were performed in adult rats and during postnatal development. The bouton volume, mitochondrial volume, and active zone area of the boutons contacting labeled somata (axosomatic synapses) were similar to those of boutons forming axoaxonic synapses with Vmes neurons but smaller than those of boutons forming axodendritic or axosomatic synapses with most other neurons. GABA+ , glycine+ , and glutamate+ boutons constituted a large majority (83%) of all boutons on labeled somata. A considerable fraction of boutons (28%) was glycine(+) , and all glycine+ boutons were also GABA+ . Bouton size remained unchanged during postnatal development. These findings suggest that the excitability of Vmes neurons is determined to a great extent by GABA, glycine, and glutamate and that the relatively lower synaptic strength of axosomatic synapses may reflect the role of the Vmes neurons in modulating orofacial motor function.
authors.affiliation: Department of Oral Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 700-412, South Korea.
authors.forename: Sang Kyoo
authors.initials: SK
authors.lastname: Paik
authors.forename: Myung Kyw
authors.initials: MK
authors.lastname: Kwak
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Bae
authors.forename: Hyun Won
authors.initials: HW
authors.lastname: Yi
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; D000831:Animals, Newborn; D018698:Glutamic Acid / Q000502:physiology; D005998:Glycine / Q000502:physiology; D008297:Male; D008410:Masticatory Muscles / Q000254:growth & development / Q000294:innervation* / Q000648:ultrastructure*; D009046:Motor Neurons / Q000378:metabolism / Q000648:ultrastructure; D009470:Muscle Spindles / Q000254:growth & development / Q000294:innervation* / Q000648:ultrastructure*; D018377:Neurotransmitter Agents / Q000502:physiology*; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014278:Trigeminal Nuclei / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
chemical_list: D018377:Neurotransmitter Agents; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005998:Glycine