title: On the vagal cardiac nerves, with special reference to the early evolution of the head-trunk interface.
abstract: The vagus nerve, or the tenth cranial nerve, innervates the heart in addition to other visceral organs, including the posterior visceral arches. In amniotes, the anterior and posterior cardiac branches arise from the branchial and intestinal portions of the vagus nerve to innervate the arterial and venous poles of the heart, respectively. The evolution of this innervation pattern has yet to be elucidated, due mainly to the lack of morphological data on the vagus in basal vertebrates. To investigate this topic, we observed the vagus nerves of the lamprey (Lethenteron japonicum), elephant shark (Callorhinchus milii), and mouse (Mus musculus), focusing on the embryonic patterns of the vagal branches in the venous pole. In the lamprey, no vagus branch was found in the venous pole throughout development, whereas the arterial pole was innervated by a branch from the branchial portion. In contrast, the vagus innervated the arterial and venous poles in the mouse and elephant shark. Based on the morphological patterns of these branches, the venous vagal branches of the mouse and elephant shark appear to belong to the intestinal part of the vagus, implying that the cardiac nerve pattern is conserved among crown gnathostomes. Furthermore, we found a topographical shift of the structures adjacent to the venous pole (i.e., the hypoglossal nerve and pronephros) between the extant gnathostomes and lamprey. Phylogenetically, the lamprey morphology is likely to be the ancestral condition for vertebrates, suggesting that the evolution of the venous branch occurred early in the gnathostome lineage, in parallel with the remodeling of the head-trunk interfacial domain during the acquisition of the neck. J. Morphol. 277:1146-1158, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Biology, Graduate School of Science, Kobe University, Kobe, 657-8501, Japan.|Evolutionary Morphology Laboratory, RIKEN, Kobe, 650-0047, Japan.|Laboratory of Veterinary Anatomy, the University of Tokyo, Tokyo, 113-8657, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Higashiyama
authors.affiliation: Evolutionary Morphology Laboratory, RIKEN, Kobe, 650-0047, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hirasawa
authors.affiliation: Evolutionary Morphology Laboratory, RIKEN, Kobe, 650-0047, Japan.|Development and Function of Inhibitory Neural Circuits, Max Planck Florida Institute for Neuroscience, Jupiter, Florida 33458, USA.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Oisi
authors.affiliation: Evolutionary Morphology Laboratory, RIKEN, Kobe, 650-0047, Japan.|Division of Biology, Hyogo College of Medicine, Nishinomiya, Hyogo, 663-8501, Japan.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Sugahara
authors.affiliation: Laboratory of Physiology, Atmosphere and Ocean Research Institute, the University of Tokyo, Chiba, 277-8564, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Hyodo
authors.affiliation: Laboratory of Veterinary Anatomy, the University of Tokyo, Tokyo, 113-8657, Japan.
authors.forename: Yoshiakira
authors.initials: Y
authors.lastname: Kanai
authors.affiliation: Evolutionary Morphology Laboratory, RIKEN, Kobe, 650-0047, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kuratani
mesh_terms: D000818:Animals; D005075:Biological Evolution; D007798:Lampreys / Q000033:anatomy & histology*; D051379:Mice / Q000033:anatomy & histology*; D012754:Sharks / Q000033:anatomy & histology*; D014630:Vagus Nerve / Q000033:anatomy & histology*
keywords: cranial nerves; heart; lamprey; vagus nerve; vertebrates