title: The location of brainstem neurons with bilateral projections to the motor nuclei of jaw openers in the cat.
abstract: Symmetrical motor output is the rule in the masticatory system. We examined morphologically how this functional symmetry might be reflected in the organization of premotor neurons that could mediate excitation of jaw-opener motoneurons. Premotor neurons projecting bilaterally to jaw-opener motoneurons by way of axon collaterals were identified by retrograde dual-labeling with cholera toxin B-conjugated fluorescein isothiocyanate (CTb-FITC) and tetramethylrhodamine (TMR). In each cat, CTb-FITC and TMR were injected into the digastric motoneuron pools, respectively, on the left and right sides. In three animals, 69-147 neurons were labeled with both tracers, comprising approximately 44% of all retrogradely labeled cells. Double-labeled cells were located bilaterally in the trigeminal oral nucleus (Vo) and the adjacent reticular formation (RF), the former containing a larger number of cells. Neurons labeled with only one tracer were also distributed bilaterally in the Vo and RF. The results indicated that the bilaterally projecting premoter neurons identified mainly in the Vo and RF represent neuronal substrates for the symmetry that characterizes most jaw movements.
authors.affiliation: Department of Physiology, Nihon University School of Dentistry, Kanda-surugadai, Chiyoda-ku, Tokyo 101-8301, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kondo
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Tsuboi
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Inage
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Iwamoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kamogawa
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology; D001933:Brain Stem / Q000166:cytology*; D002415:Cats; D007568:Jaw / Q000166:cytology / Q000294:innervation* / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D012018:Reflex