title: Postnatal changes in glutamatergic inputs of jaw-closing motoneuron dendrites.
abstract: Dendrites of masseter (jaw-closing) motoneurons (MMNs) are well developed and ramify extensively throughout the trigeminal motor nucleus and often extend into the adjacent reticular formation. It is possible that the dendrites have active properties, which are altered with the development of the orofacial musculoskeletal system. Thus, we examined the changes in somatic voltage responses evoked by photostimulation of the MMN dendrites by laser photolysis of caged glutamate from postnatal day (P) 2-5 and 9-12 rats. We photostimulated 39 spots that were arranged around each recorded neuron in a concave shape and found that the dendritic stimulation induced somatic depolarization in the presence of tetrodotoxin in all MMNs. With increasing photostimulation intensity, the responses grew in amplitude up to a certain threshold, where a step-like increase in amplitude occurred. In 75% of P2-5 MMNs, the step-like increase in amplitude, which was blocked by 20μM D(-)-2-amino-5-phosphonovaleric acid application, corresponded to the NMDA spikes/plateau potentials. In contrast, at P9-12 the responses became significantly smaller in amplitude and shorter in duration and only one neuron out of 12 MMNs showed NMDA spikes/plateau potentials. These results suggest that the glutamatergic responses evoked by photostimulation of the MMN dendrites change during the first two postnatal weeks, and these changes may be involved in the transition from suckling to chewing during postnatal development.
authors: Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan; Department of Periodontology, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ohta-ku, Tokyo, 145-8515, Japan.
authors: Shoko
authors: S
authors: Nagata
authors: Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan. Electronic address: snaka@dent.showa-u.ac.jp.
authors: Shiro
authors: S
authors: Nakamura
authors: Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan.
authors: Kiyomi
authors: K
authors: Nakayama
authors: Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan.
authors: Ayako
authors: A
authors: Mochizuki
authors: Department of Periodontology, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ohta-ku, Tokyo, 145-8515, Japan.
authors: Matsuo
authors: M
authors: Yamamoto
authors: Department of Oral Physiology, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan.
authors: Tomio
authors: T
authors: Inoue
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000166:cytology / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology*; D003712:Dendrites / Q000187:drug effects / Q000502:physiology*; D016503:Drug Delivery Systems; D018698:Glutamic Acid / Q000008:administration & dosage / Q000378:metabolism*; D007834:Lasers; D008406:Masseter Muscle / Q000254:growth & development / Q000294:innervation* / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D016202:N-Methylaspartate / Q000378:metabolism; D056347:Neuroanatomical Tract-Tracing Techniques; D018377:Neurotransmitter Agents / Q000008:administration & dosage; D018408:Patch-Clamp Techniques; D017208:Rats, Wistar; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D046509:Tissue Culture Techniques
chemical_list: D018377:Neurotransmitter Agents; D026941:Sodium Channel Blockers; D018698:Glutamic Acid; D013779:Tetrodotoxin; D016202:N-Methylaspartate
keywords: Active properties; Dendrites; Masseter motoneurons; NMDA spikes/plateau potentials; Photostimulation; Postnatal development