title: Monosynaptic projections from the nucleus retroambiguus region to laryngeal motoneurons in the rhesus monkey.
abstract: Vocalization and straining-related activities require the activation of laryngeal muscles. The control of laryngeal muscles during these activities is thought to be mediated by a pathway from the periaqueductal gray via premotor neurons in the nucleus retroambiguus to laryngeal motoneurons in the nucleus ambiguus. However, direct contacts between the nucleus retroambiguus and laryngeal motoneurons have never been demonstrated anatomically. Moreover, data in primates about the nucleus retroambiguus-nucleus ambiguus pathway are lacking. Therefore, the present study examines the projection from the nucleus retroambiguus region to laryngeal motoneurons in the rhesus monkey at the light and electron microscopic levels. Injections with wheat germ agglutinin-horseradish peroxidase were made into the nucleus retroambiguus in five rhesus monkeys to anterogradely label fibers in the nucleus ambiguus. In two of these animals, the cricothyroid muscle was injected with cholera toxin subunit b to identify the motoneurons that supply it. The results show that the nucleus retroambiguus region most densely projects to the compact formation of the nucleus ambiguus, whereas cricothyroid motoneurons, which surround the compact formation, receive a moderate projection. The projections are bilateral, with a contralateral predominance. Ultrastructurally, anterogradely labeled terminal profiles from the nucleus retroambiguus contact cholera toxin subunit b-labeled dendrites of cricothyroid motoneurons. The terminal profiles contain primarily spherical vesicles and form asymmetrical contacts with cricothyroid motoneurons. This study demonstrates that the nucleus retroambiguus region projects to the nucleus ambiguus in the primate. Some of these projections include monosynaptic connections to laryngeal motoneurons. This pathway is important for the control of the vocal folds during vocalization and straining-related activities.
authors.affiliation: Department of Anatomy, University of California at San Francisco, 94143-0452, USA. vdhorst@phy.ucsf.edu
authors.forename: V G
authors.initials: VG
authors.lastname: VanderHorst
authors.forename: E
authors.initials: E
authors.lastname: Terasawa
authors.forename: H J
authors.initials: HJ
authors.lastname: Ralston
mesh_terms: D000818:Animals; D002772:Cholera Toxin; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D007821:Laryngeal Muscles / Q000294:innervation / Q000502:physiology; D007823:Laryngeal Nerves / Q000502:physiology / Q000648:ultrastructure*; D008253:Macaca mulatta / Q000033:anatomy & histology* / Q000502:physiology; D008526:Medulla Oblongata / Q000502:physiology / Q000648:ultrastructure*; D008854:Microscopy, Electron; D009046:Motor Neurons / Q000502:physiology / Q000648:ultrastructure*; D009434:Neural Pathways / Q000502:physiology / Q000648:ultrastructure*; D010487:Periaqueductal Gray / Q000166:cytology / Q000502:physiology; D017729:Presynaptic Terminals / Q000502:physiology / Q000648:ultrastructure; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure*; D014828:Vocalization, Animal / Q000502:physiology*; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate
chemical_list: D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D002772:Cholera Toxin