title: Involvement of histaminergic inputs in the jaw-closing reflex arc.
abstract: Histamine receptors are densely expressed in the mesencephalic trigeminal nucleus (MesV) and trigeminal motor nucleus. However, little is known about the functional roles of neuronal histamine in controlling oral-motor activity. Thus, using the whole-cell recording technique in brainstem slice preparations from Wistar rats aged between postnatal days 7 and 13, we investigated the effects of histamine on the MesV neurons innervating the masseter muscle spindles and masseter motoneurons (MMNs) that form a reflex arc for the jaw-closing reflex. Bath application of histamine (100 μM) induced membrane depolarization in both MesV neurons and MMNs in the presence of tetrodotoxin, whereas histamine decreased and increased the input resistance in MesV neurons and MMNs, respectively. The effects of histamine on MesV neurons and MMNs were mimicked by an H1 receptor agonist, 2-pyridylethylamine (100 μM). The effects of an H2 receptor agonist, dimaprit (100 μM), on MesV neurons were inconsistent, whereas MMNs were depolarized without changes in the input resistance. An H3 receptor agonist, immethridine (100 μM), also depolarized both MesV neurons and MMNs without changing the input resistance. Histamine reduced the peak amplitude of postsynaptic currents (PSCs) in MMNs evoked by stimulation of the trigeminal motor nerve (5N), which was mimicked by 2-pyridylethylamine but not by dimaprit or immethridine. Moreover, 2-pyridylethylamine increased the failure rate of PSCs evoked by minimal stimulation and the paired-pulse ratio. These results suggest that histaminergic inputs to MesV neurons through H1 receptors are involved in the suppression of the jaw-closing reflex although histamine depolarizes MesV neurons and/or MMNs.
authors.affiliation: Department of Oral Physiology, Showa University School of Dentistry, Shinagawa-ku, Tokyo, Japan; Department of Pediatric Dentistry, Showa University School of Dentistry, Oota-ku, Tokyo, Japan.
authors.forename: Chikako
authors.initials: C
authors.lastname: Gemba
authors.affiliation: Department of Oral Physiology, Showa University School of Dentistry, Shinagawa-ku, Tokyo, Japan;
authors.forename: Kiyomi
authors.initials: K
authors.lastname: Nakayama
authors.affiliation: Department of Oral Physiology, Showa University School of Dentistry, Shinagawa-ku, Tokyo, Japan;
authors.forename: Shiro
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Department of Oral Physiology, Showa University School of Dentistry, Shinagawa-ku, Tokyo, Japan;
authors.forename: Ayako
authors.initials: A
authors.lastname: Mochizuki
authors.affiliation: Department of Pediatric Dentistry, Showa University School of Dentistry, Oota-ku, Tokyo, Japan inouet@dent.showa-u.ac.jp.
authors.forename: Mitsuko
authors.initials: M
authors.lastname: Inoue
authors.affiliation: Department of Oral Physiology, Showa University School of Dentistry, Shinagawa-ku, Tokyo, Japan;
authors.forename: Tomio
authors.initials: T
authors.lastname: Inoue
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001703:Biophysics; D001933:Brain Stem / Q000166:cytology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D006632:Histamine / Q000378:metabolism* / Q000494:pharmacology; D018494:Histamine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009475:Neurons, Afferent / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D011930:Reaction Time / Q000187:drug effects; D026941:Sodium Channel Blockers / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology; D014276:Trigeminal Nerve / Q000502:physiology
chemical_list: D018494:Histamine Agents; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin; D006632:Histamine
keywords: histamine; jaw-closing reflex; masseter motoneuron; mesencephalic trigeminal nucleus; patch clamp