The somatotopic organization of the olfactory bulb in elasmobranchs

Authors

  • Tricia L. Meredith,

    Corresponding author
    1. Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
    2. Department of Physiology and Biophysics, University of Miami, Leonard M. Miller School of Medicine, Miami, Florida 33136
    • Department of Physiology and Biophysics, University of Miami, Leonard M. Miller School of Medicine, Rosenstiel Medical Sciences Building, 1600 NW 10th Ave., Miami, FL 33136
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  • Stephen M. Kajiura,

    1. Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida 33431
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  • Anne Hansen

    1. Department of Cell and Developmental Biology, University of Colorado Denver, Anschutz Medical Campus, Aurora, Colorado 80045
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Abstract

The olfactory bulbs (OBs) are bilaterally paired structures in the vertebrate forebrain that receive and process odor information from the olfactory receptor neurons (ORNs) in the periphery. Virtually all vertebrate OBs are arranged chemotopically, with different regions of the OB processing different types of odorants. However, there is some evidence that elasmobranch fishes (sharks, rays, and skates) may possess a gross somatotopic organization instead. To test this hypothesis, we used histological staining and retrograde tracing techniques to examine the morphology and organization of ORN projections from the olfactory epithelium (OE) to the OB in three elasmobranch species with varying OB morphologies. In all three species, glomeruli in the OB received projections from ORNs located on only the three to five lamellae situated immediately anterior within the OE. These results support that the gross arrangement of the elasmobranch OB is somatotopic, an organization unique among fishes and most other vertebrates. In addition, certain elasmobranch species possess a unique OB morphology in which each OB is physically subdivided into two or more “hemi-olfactory bulbs.” Somatotopy could provide a preadaptation which facilitated the evolution of olfactory hemibulbs in these species. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.

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