title: The centrifugal visual system of a palaeognathous bird, the Chilean Tinamou (Nothoprocta perdicaria).
abstract: The avian centrifugal visual system, which projects from the brain to the retina, has been intensively studied in several Neognathous birds that have a distinct isthmo-optic nucleus (ION). However, birds of the order Palaeognathae seem to lack a proper ION in histologically stained brain sections. We had previously reported in the palaeognathous Chilean Tinamou (Nothoprocta perdicaria) that intraocular injections of Cholera Toxin B subunit retrogradely label a considerable number of neurons, which form a diffuse isthmo-optic complex (IOC). In order to better understand how this IOC-based centrifugal visual system is organized, we have studied its major components by means of in vivo and in vitro tracing experiments. Our results show that the IOC, though structurally less organized than an ION, possesses a dense core region consisting of multipolar neurons. It receives afferents from neurons in L10a of the optic tectum, which are distributed with a wider interneuronal spacing than in Neognathae. The tecto-IOC terminals are delicate and divergent, unlike the prominent convergent tecto-ION terminals in Neognathae. The centrifugal IOC terminals in the retina are exclusively divergent, resembling the terminals from "ectopic" centrifugal neurons in Neognathae. We conclude that the Tinamou's IOC participates in a comparable general IOC-retina-TeO-IOC circuitry as the neognathous ION. However, the connections between the components are structurally different and their divergent character suggests a lower spatial resolution. Our findings call for further comparative studies in a broad range of species for advancing our understanding of the evolution, plasticity and functional roles of the avian centrifugal visual system.
authors.affiliation: Lehrstuhl für Zoologie, Technische Universität München, Freising-Weihenstephan, Germany.
authors.forename: Quirin
authors.identifier: http://orcid.org/0000-0003-1431-5591
authors.initials: Q
authors.lastname: Krabichler
authors.affiliation: Lehrstuhl für Zoologie, Technische Universität München, Freising-Weihenstephan, Germany.
authors.forename: Tomas
authors.initials: T
authors.lastname: Vega-Zuniga
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Denisse
authors.initials: D
authors.lastname: Carrasco
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.
authors.forename: Maximo
authors.initials: M
authors.lastname: Fernandez
authors.affiliation: Lehrstuhl für Zoologie, Technische Universität München, Freising-Weihenstephan, Germany.
authors.forename: Cristián
authors.initials: C
authors.lastname: Gutiérrez-Ibáñez
authors.affiliation: Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile.|Facultad de Medicina, Universidad Finis Terrae, Santiago, Chile.
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Marín
authors.affiliation: Lehrstuhl für Zoologie, Technische Universität München, Freising-Weihenstephan, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Luksch
mesh_terms: D000818:Animals; D001717:Birds; D002677:Chile; D005260:Female; D008297:Male; D046108:Palaeognathae / Q000033:anatomy & histology / Q000502:physiology*; D012160:Retina / Q000166:cytology / Q000502:physiology*; D013045:Species Specificity; D013477:Superior Colliculi / Q000166:cytology / Q000502:physiology*; D014795:Visual Pathways / Q000166:cytology / Q000502:physiology*
keywords: RRID:AB_10013220; RRID:AB_2315144; RRID:AB_2336126; RRID:AB_2534088; RRID:AB_477329; association amacrine cells; divergent terminals; ectopic centrifugal neurons; isthmo-optic nucleus; optic tectum; retinopetal; tecto-isthmal; tyramide signal amplification