Diverse contributions of Tas1r2/Tas2rs within the rat and mouse soft palate to sweet and bitter neural responses.
Neural responses to sweet and bitter stimuli in the rat and mouse are compared to the expression of the molecular taste receptors, Tas1r2/Tas2rs. Integrated taste responses from the greater superficial petrosal nerve (GSP) innervating the soft palate (SP) and the chorda tympani (CT) nerve innervating the fungiform papillae (FF) were recorded in C57BL mice and SD rats. The sum of the phasic and tonic response magnitudes (SRM) was calculated by summating all relative mean responses to a concentration series of QHCl (10(-6)-10(-2)M) or Suc (10(-4)-1.0M). Molecular expression was analyzed by double-colored in situ hybridization for Gα-gustducin with Tas1r2 or Tas2rs in the SP and FF. The vast majority of cells expressing Tas1r2 or Tas2rs were included in Gα-gustducin-expressing cells in the SP of both species. Unexpectedly, a comparison between species revealed that the SRM from the GSP is not positively correlated with receptor expression in the SP. In the rat SP, the percentage of Tas2rs with Gα-gustducin (Tas2rs/gust, 65%) was twice larger than that for Tas1r2/gust (33%), while the SRM to Suc in the rat GSP was 1.5 times (tonic and phasic) larger than that to QHCl. In the mouse SP, the percentage of Tas2rs/gust (46%) was less than that in the rat and similar to that of Tas1r2/gust (40%). However, the SRM to QHCl in the mouse GSP was 2.4 (phasic) and 4.7 (tonic) times larger than to Suc. On the other hand, threshold to Suc in the rat GSP was 10(-3)M, one log unit lower than in mouse, and the threshold to QHCl in the mouse GSP was 10(-6)M, one log unit lower than in rat. These results suggest that the robust GSP response to Suc in rat and to QHCl in mouse likely do not depend upon a large number of taste cells expressing the taste receptors Tas1r2 for Suc or Tas2rs for QHCl, but upon a higher density of Tas1r2/Tas2rs within the respective taste cells of the two species.
Department of Oral Physiology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan.
Hiroshi
H
Tomonari
Department of Oral Physiology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan. Electronic address: hmiura@dent.kagoshima-u.ac.jp.
Hirohito
H
Miura
Department of Oral Physiology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan.
Makoto
M
Ooki
Department of Oral Physiology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan.
Ayumi
A
Nakayama
Department of Oral Physiology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan.
Shuitsu
S
Harada
D000818:Animals; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D008297:Male; D008810:Mice, Inbred C57BL; D010160:Palate, Soft / Q000166:cytology / Q000294:innervation / Q000378:metabolism*; D011803:Quinine / Q000494:pharmacology; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D013045:Species Specificity; D013395:Sucrose / Q000494:pharmacology; D013649:Taste; D015293:Transducin / Q000378:metabolism; D000098706:Taste Receptors, Type 2
D043562:Receptors, G-Protein-Coupled; C431926:taste receptors, type 1; D000098706:Taste Receptors, Type 2; C075192:gustducin; D013395:Sucrose; D011803:Quinine; C524407:GNAT3 protein, mouse; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin
Bitter; Chorda tympani nerve; Greater superficial petrosal nerve; Sweet; Taste receptor