Ultrastructural analysis of a putative magnetoreceptor in the beak of homing pigeons

Authors

  • Gerta Fleissner,

    Corresponding author
    1. Zoologisches Institut, J. W. Goethe-Universität Frankfurt am Main, D-60054 Frankfurt am Main, Germany
    • Zoologisches Institut, J. W. Goethe-Universität Frankfurt am Main, Siesmayerstr. 70, D-60054 Frankfurt am Main, Germany
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  • Elke Holtkamp-Rötzler,

    1. Zoologisches Institut, J. W. Goethe-Universität Frankfurt am Main, D-60054 Frankfurt am Main, Germany
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  • Marianne Hanzlik,

    1. Institut für Geophysik, Ludwig Maximilians-Universität München, D-80333 Munich, Germany
    2. Institut für Technische Chemie, Technische Universität München, D-85748 Garching, Germany
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  • Michael Winklhofer,

    1. Institut für Geophysik, Ludwig Maximilians-Universität München, D-80333 Munich, Germany
    2. School of Ocean & Earth Science, University of Southampton, Southampton Oceanography Centre, Southampton, SO14 3ZH, United Kingdom
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  • Günther Fleissner,

    1. Zoologisches Institut, J. W. Goethe-Universität Frankfurt am Main, D-60054 Frankfurt am Main, Germany
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  • Nikolai Petersen,

    1. Institut für Geophysik, Ludwig Maximilians-Universität München, D-80333 Munich, Germany
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  • Wolfgang Wiltschko

    1. Zoologisches Institut, J. W. Goethe-Universität Frankfurt am Main, D-60054 Frankfurt am Main, Germany
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Abstract

With the use of different light and electron microscopic methods, we investigated the subcellular organization of afferent trigeminal terminals in the upper beak of the homing pigeon, Columba livia, which are about 5 μm in diameter and contain superparamagnetic magnetite (SPM) crystals. The SPM nanocrystals are assembled in clusters (diameter, ∼1–2 μm). About 10 to 15 of these clusters occur inside one nerve terminal, arranged along the cell membrane. Each SPM cluster is embedded in a solid fibrous cup, open towards the cell surface, to which the cluster adheres by delicate fiber strands. In addition to the SPM clusters, a second inorganic iron compound has been identified: noncrystalline platelets of iron phosphate (about 500 nm wide and long and maximally 100 nm thick) that occur along a fibrous core of the terminal. The anatomic features suggested that these nerve endings could detect small intensity changes of the geomagnetic field. Such stimuli can induce deformations of the SPM clusters, which could be transduced into primary receptor potentials by mechanosensitive membrane receptor channels. The subepidermal fat cells surrounding the nerve endings prevent the inside from external mechanical stimuli. These structural findings corresponded to conclusions inferred from rock magnetic measurements, theoretical calculations, model experiments, and behavioral data, which also matched previous electrophysiologic recordings from migratory birds. J. Comp. Neurol. 458:350–360, 2003. © 2003 Wiley-Liss, Inc.

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