Elsevier

Neuroscience

Volume 7, Issue 4, April 1982, Pages 809-836
Neuroscience

Neuronal architecture in nucleus magnocellularis of the chicken auditory system with observations on nucleus laminaris: A light and electron microscope study

https://doi.org/10.1016/0306-4522(82)90045-8Get rights and content

Abstract

This report presents the major structural features of neurons and their afferent input in nucleus magnocellularis, the avian homologue of the mammalian anteroventral cochlear nucleus. Results of light-microscope observations, as seen in Golgi, Nissl, and normal fiber preparations, as well as ultrastructural morphology are reported. In addition, cells and axons in nucleus laminaris, the presumed homologue of the mammalian medial superior olivary nucleus, are also described.

In Golgi-impregnated material, the mature principal cell in nucleus magnocellularis has an ovoid soma encrusted with somatic spines. A dendrite, when present, emerges from the cell soma, travels for a short distance and breaks into a tuft of stubby terminal branches. Foremost among the afferents to nucleus magnocellularis are auditory nerve axons that terminate in large, axosomatic endings, or endbulbs, covering a large portion of the somatic surface. Other afferents, which also end in relation to the perikaryon, are of undetermined and perhaps multiple origins. The neurons resemble the bushy cells of the mammalian anteroventral cochlear nucleus. Evidence is presented that individual axons from the nucleus magnocellularis bifurcate and send branches to the nucleus laminaris bilaterally, thus placing constraints on the binaural interactions possibly involved in lateralization functions.

In electron micrographs, the end-bulbs appear as large, elongate structures which can cover a third of the cell soma. Multiple sites of synaptic specialization occur along these terminals. The synaptic membrane complexes may form directly on the cell body or on the sides or crests of somatic spines. These complexes are characterized by asymmetric membrane densities with a cluster of clear, spherical vesicles on the axonal side. Other small terminal profiles are also present on the somata receiving the end-bulbs. Dendritic profiles are scarce, in agreement with observations in Golgi impregnations.

The structural findings indicate that the medial part of the nucleus magnocellularis is homologous to the anterior part of the mammalian anteroventral cochlear nucleus in that the neurons of nucleus magnocellularis are homologous to the bushy cells of the cat. On this basis, the cells in nucleus magnocellularis could faithfully preserve the acoustic response patterns generated in the auditory nerve. This should, in turn, allow a secure relay of bilateral latency differences essential for binaural interactions in the nucleus laminaris.

Reference (44)

  • BoordR.L. et al.

    The distribution of primary lagenar fibers within the vestibular nuclear complex of the pigeon

    Brain Behav. Evol.

    (1974)
  • BoordR.L. et al.

    Projection of the cochlear and lagenar nerves on the cochlear nuclei of the pigeon

    J. comp. Neurol.

    (1963)
  • BourkT.R.

    Electrical responses of neural units in the anteroventral cochlear nucleus of the cat

  • BrandisF.

    Untersuchungenüber das Gehirn der Vogel—II. Theil: Ursprung der Nerven der Medulla oblongata

    Arch. mikr. Anat.

    (1894)
  • BrawerJ.R. et al.

    Relations between auditory nerve endings and cell types in the cat's anteroventral cochlear nucleus seen with the Golgi method and Nomarski optics

    J. comp. Neurol.

    (1975)
  • BrawerJ.R. et al.

    The neuronal architecture of the cochlear nucleus of the cat

    J. comp. Neurol.

    (1974)
  • FeldmanM.L. et al.

    The projection of the acoustic nerve to the ventral cochlear nucleus of the rat. A Golgi study

    J. comp. Neurol.

    (1969)
  • HarrisonJ.M. et al.

    The anterior ventral cochlear nucleus

    J. comp. Neurol.

    (1965)
  • IbataY. et al.

    The fine structure of synapses in relation to the large spherical neurons in the anterior ventral cochlear nucleus of the cat

    J. Neurocytol.

    (1976)
  • JacksonJ.R.H. et al.

    Rapid transneuronal degeneration following cochlea removal in chickens

    Anat. Rec.

    (1976)
  • JeffressL.A.

    A place theory of sound localization

    J. comp. physiol. Psychol.

    (1948)
  • KartenH.J. et al.

    A Stereotaxic Atlas of the Brain of the Pigeon (Columba livia)

    (1967)
  • Cited by (130)

    • 2.36 - Coding of Spatial Information

      2020, The Senses: A Comprehensive Reference: Volume 1-7, Second Edition
    • Structure and function of myelinated axons

      2020, Patterning and Cell Type Specification in the Developing CNS and PNS: Comprehensive Developmental Neuroscience, Second Edition
    • Structure and Function of Myelinated Axons

      2013, Comprehensive Developmental Neuroscience: Patterning and Cell Type Specification in the Developing CNS and PNS
    View all citing articles on Scopus
    *

    Present address: Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, U.S.A.

    View full text