Expression of metabotropic glutamate receptor group I in rat gustatory papillae.
Taste-metabotropic glutamate receptor 4 (taste-mGluR4) and the heteromers of T1R1 and T1R3 are candidate receptors involved in the sense of umami (monosodium glutamate) taste. Although the expression of group III mGluRs (taste-mGluR4) has been demonstrated in taste tissues, no mention has been made of the expression of group I mGluRs (mGluR1 and mGluR5) in taste tissues. We examined the expression of mGluR1 and mGluR5 in rat gustatory tissues by using reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, immunohistochemistry and immunoelectron microscopy. RT-PCR assay showed that mGluR1 alpha and mGluR1 beta mRNAs were expressed in circumvallate papillae, but mGluR5 mRNA was not expressed. The positive signals of mGluR1 mRNA were detected only in circumvallate taste buds by in situ hybridization analysis. In cryosections of fungiform, foliate and circumvallate papillae, the antibody against mGluR1 alpha gave intense labeling on the taste hairs in all taste pores examined. In the developing taste buds, the positive signals of mGluR1alpha in taste hairs gradually increased with the increase in number of taste bud cells. These results show that, in addition to taste-mGluR4 and the heteromer of T1R1 and T1R3, mGluR1 alpha may function as a receptor for glutamate (umami) taste sensation.
Toyono
Takashi
T
Department of Oral Anatomy and Neurobiology, Kyushu Dental College, Kokurakita-ku, 803-8580, Kitakyushu, Japan. toyono@kyu-dent.ac.jp
Seta
Yuji
Y
Kataoka
Shinji
S
Kawano
Shintaro
S
Shigemoto
Ryuichi
R
Toyoshima
Kuniaki
K
D000818:Animals; D001923:Brain Chemistry; D002847:Chromatography, Agarose; D004848:Epithelium / Q000737:chemistry; D005260:Female; D015870:Gene Expression; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007633:Keratins / Q000032:analysis; D008297:Male; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008858:Microscopy, Phase-Contrast; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000032:analysis / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013650:Taste Buds / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D014059:Tongue / Q000737:chemistry / Q000166:cytology / Q000378:metabolism
C578937:Grm5 protein, rat; D020033:Protein Isoforms; D012333:RNA, Messenger; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; C104077:metabotropic glutamate receptor type 1; D007633:Keratins