Expression of neurotrophins and Trk receptors in the developing, adult, and regenerating avian cochlea

Authors

  • Ulla Pirvola,

    Corresponding author
    1. Institute of Biotechnology, University of Helsinki, P.O. Box 56 (Viikinkaari 9), FIN-00014, Helsinki, Finland
    2. Department of Otorhinolaryngology, University of Helsinki, FIN-00029 Helsinki, Finland
    • Institute of Biotechnology, University of Helsinki, P.O. Box 56 (Viikinkaari 9), FIN-00014, Helsinki, Finland
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  • Finn Hallböök,

    1. Department of Developmental Neuroscience, BMC, University of Uppsala, S-75123 Uppsala, Sweden
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  • Liang Xing-Qun,

    1. Institute of Biotechnology, University of Helsinki, P.O. Box 56 (Viikinkaari 9), FIN-00014, Helsinki, Finland
    2. Department of Otorhinolaryngology, University of Kuopio, FIN-70211 Kuopio, Finland
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  • Jussi Virkkala,

    1. Institute of Biotechnology, University of Helsinki, P.O. Box 56 (Viikinkaari 9), FIN-00014, Helsinki, Finland
    2. Department of Otorhinolaryngology, University of Helsinki, FIN-00029 Helsinki, Finland
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  • Mart Saarma,

    1. Institute of Biotechnology, University of Helsinki, P.O. Box 56 (Viikinkaari 9), FIN-00014, Helsinki, Finland
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  • Jukka Ylikoski

    1. Department of Otorhinolaryngology, University of Helsinki, FIN-00029 Helsinki, Finland
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Abstract

We studied the expression of neurotrophins and their Trk receptors in the chicken cochlea. Based on in situ hybridization, brain-derived neurotrophic factor (BDNF) is the major neurotrophin there, in contrast to the mammalian cochlea, where neurotrophin-3 (NT-3) predominates. NT-3 mRNA labeling was weak and found only during a short time period in the early cochles. During embryogenesis, BDNF mRNA was first seen in early differentiating hair cells. Afferent cochlear neurons expressed trkB mRNA from the early stages of gangliogenesis onward. In accordance, in vitro, BDNF promoted survival of dissociated neurons and stimulated neuritogenesis from ganglionic explants. High levels of BDNF mRNA in hair cells and trkB mRNA in cochlear neurons persisted in the mature cochlea. In addition, mRNA for the truncated TrkB receptor was expressed in nonneuronal cells, specifically in supporting cells, located adjacent to the site of BDNF synthesis and nerve endings. Following acoustic trauma, regenerated hair cells acquired BDNF mRNA expression at early stages of differentiation. Truncated trkB mRNA was lost from supporting cells that regenerated into hair cells. High levels of BDNF mRNA persisted in surviving hair cells and trkB mRNA in cochlear neurons after noise exposure. These results suggest that in the avian cochlea, peripheral target-derived BDNF contributes to the onset and maintenance of hearing function by supporting neuronal survival and regulating the (re)innervation process. Truncated TrkB receptors may regulate the BDNF concentration available to neurites, and they might have an important role during reinnervation. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 1019–1033, 1997

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