Expression of G proteins in the olfactory receptor neurons of the newt Cynops pyrrhogaster: Their unique projection into the olfactory bulbs

Authors

  • Tomoaki Nakada,

    Corresponding author
    1. Department of Comparative and Behavioral Medicine, Faculty of Veterinary Medicine, Nippon Veterinary and Life Science University, Tokyo, Japan
    • Correspondence to: Tomoaki Nakada, Ph.D., Department of Comparative and Behavioral Medicine, Faculty of Veterinary Medicine, Nippon Veterinary and Life Science University, 1-7-1 Kyonancho, Musashino, Tokyo 180–8602, Japan. E-mail: tnakada@nvlu.ac.jp

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  • Kimiko Hagino-Yamagishi,

    1. Integrated Brain Function Project, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
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  • Koki Nakanishi,

    1. Department of Comparative and Behavioral Medicine, Faculty of Veterinary Medicine, Nippon Veterinary and Life Science University, Tokyo, Japan
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  • Makoto Yokosuka,

    1. Department of Comparative and Behavioral Medicine, Faculty of Veterinary Medicine, Nippon Veterinary and Life Science University, Tokyo, Japan
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  • Toru R. Saito,

    1. Department of Comparative and Behavioral Medicine, Faculty of Veterinary Medicine, Nippon Veterinary and Life Science University, Tokyo, Japan
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  • Fumiyo Toyoda,

    1. Department of Physiology, Nara Medical University, Nara, Japan
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  • Itaru Hasunuma,

    1. Department of Biology, Faculty of Science, Toho University, Chiba, Japan
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  • Takashi Nakakura,

    1. Department of Anatomy, Graduate School of Medicine, Teikyo University, Tokyo, Japan
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  • Sakae Kikuyama

    1. Department of Biology, Faculty of Science, Toho University, Chiba, Japan
    2. Department of Biology, Faculty of Education and Integrated Sciences, Waseda University, Tokyo, Japan
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ABSTRACT

We analyzed the expression of G protein α subunits and the axonal projection into the brain in the olfactory system of the semiaquatic newt Cynops pyrrhogaster by immunostaining with antibodies against Gαolf and Gαo, by in situ hybridization using probes for olf, o, and i2, and by neuronal tracing with DiI and DiA. The main olfactory epithelium (OE) consists of two parts, the ventral OE and dorsal OE. In the ventral OE, the Gαolf- and Gαo-expressing neurons are located in the apical and basal zone of the OE, respectively. This zonal expression was similar to that of the OE in the middle cavity of the fully aquatic toad Xenopus laevis. However, the Gαolf- and Gαo-expressing neurons in the newt ventral OE project their axons toward the main olfactory bulb (MOB) and the accessory olfactory bulb (AOB), respectively, whereas in Xenopus, the axons of both neurons project solely toward the MOB. In the dorsal OE of the newt, as in the principal cavity of Xenopus, the majority of the neurons express Gαolf and extend their axons into the MOB. In the vomeronasal organ (VNO), the neurons mostly express Gαo. These neurons and quite a few Gαolf-expressing neurons project their axons toward the AOB. This feature is similar to that in the terrestrial toad Bufo japonicus and is different from that in Xenopus, in which VNO neurons express solely Gαo, although their axons invariably project toward the AOB. We discuss the findings in the light of diversification and evolution of the vertebrate olfactory system. J. Comp. Neurol. 522:3501–3519, 2014. © 2014 Wiley Periodicals, Inc.

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