Tonotopic gradients of Eph family proteins in the chick nucleus laminaris during synaptogenesis

Authors

  • Abigail L. Person,

    1. Neurobiology and Behavior Program, University of Washington, Seattle, Washington 98195
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  • Douglas Pat Cerretti,

    1. Department of Vascular Biology, Amgen Corporation, Seattle, Washington 98101
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  • Elena B. Pasquale,

    1. Neurobiology Program, Burnham Institute, La Jolla, California 92037
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  • Edwin W. Rubel,

    1. Department of Physiology and Biophysics, University of Washington, Seattle, Washington 98195
    2. Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology, Head and Neck Surgery, University of Washington, Seattle, Washington 98195
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  • Karina S. Cramer

    Corresponding author
    1. Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology, Head and Neck Surgery, University of Washington, Seattle, Washington 98195
    Current affiliation:
    1. Department of Neurobiology and Behavior, University of California, Irvine, 2205 McGaugh Hall, Irvine, CA 92697-4550
    • Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology, Head and Neck Surgery, University of Washington, Seattle, Washington 98195
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Abstract

Topographically precise projections are established early in neural development. One such topographically organized network is the auditory brainstem. In the chick, the auditory nerve transmits auditory information from the cochlea to nucleus magnocellularis (NM). NM in turn innervates nucleus laminaris (NL) bilaterally. These projections preserve the tonotopy established at the level of the cochlea. We have begun to examine the expression of Eph family proteins during the formation of these connections. Optical density measurements were used to describe gradients of Eph proteins along the tonotopic axis of NL in the neuropil, the somata, and the NM axons innervating NL at embryonic day 10, when synaptic connections from NM to NL are established. At E10–11, NL dorsal neuropil expresses EphA4 at a higher concentration in regions encoding high frequency sounds, decreasing in concentration monotonically toward the low frequency (caudolateral) end. In the somata, both EphA4 and ephrin-B2 are concentrated at the high frequency end of the nucleus. These tonotopic gradients disappear between E13 and E15, and expression of these molecules is completely downregulated by hatching. The E10–11 patterns run counter to an apparent gradient in dendrite density, as indicated by microtubule associated protein 2 (MAP2) immunolabeling. Finally, ephrin-B2 is also expressed in a gradient in tissue ventral to the NL neuropil. Our findings thus suggest a possible conserved mechanism for establishing topographic projections in diverse sensory systems. These results of this study provide a basis for the functional examination of the role of Eph proteins in the formation of tonotopic maps in the brainstem. © 2004 Wiley Periodicals, Inc. J Neurobiol 60: 28–39, 2004

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