P2X2- and P2X3-positive fibers in fungiform papillae originate from the chorda tympani but not the trigeminal nerve in rats and mice

Authors

  • Yusuke Ishida,

    Corresponding author
    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
    • Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya 467-8601, Japan
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  • Shinya Ugawa,

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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  • Takashi Ueda,

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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  • Takahiro Yamada,

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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  • Yasuhiro Shibata,

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
    2. Department of Urology, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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  • Aki Hondoh,

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
    2. Department of Otorhinolaryngology, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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  • Kiyoshi Inoue,

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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  • Yong Yu,

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
    2. Department of Neurosurgery, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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  • Shoichi Shimada

    1. Department of Neurobiology and Anatomy, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan
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Abstract

The subtype 2 and subtype 3 ionotropic purinergic receptors (P2X receptors) are crucial for gustation, but the distribution of these receptors in the geniculate ganglion (GG) and their colocalization in tongue papillae remain unknown. Here we investigated the expression and colocalization of P2X2 and P2X3 receptors in the GG and fungiform papillae in rats and mice by using in situ hybridization and immunohistochemistry. In both species, P2X2 transcripts and immunoreactivity were detected in approximately 50–60% of GG neuronal somata, whereas those of P2X3 were observed in almost all neurons. In each fungiform papilla, immunoreactivity for both receptors was mostly colocalized and was seen in nerve fibers and their bundles concentrated in the taste buds. Because it is well known that the P2X receptors are involved in not only taste but also nociception, we determined whether the expression originated from the chorda tympani nerve (CT, gustatory) or trigeminal nerve (somatosensory) by cutting the CT in both animals. Most P2X2 and P2X3 immunoreactivity in the fungiform papillae was abolished after transection, although the nerve fiber immunoreactivity of transient receptor potential V1 (a marker of somatosensory nerve fibers) remained unchanged, indicating that most fungiform papillae nerve fibers with P2X2 and P2X3 receptors were derived from CT. Taken together, these findings suggest that most P2X2 and P2X3 receptors in fungiform papillae are used for gustation rather than somatosensation. J. Comp. Neurol. 514:131–144, 2009. © 2009 Wiley-Liss, Inc.

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