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Yuzo Ninomiya

Publications and source records attributed to Yuzo Ninomiya.

At least 19 recordsLinked to original sources
PubMed2006

Induction of salivary kallikreins by the diet containing a sweet-suppressive peptide, gurmarin, in the rat.

Gymnema sylvestre (gymnema) contains gurmarin that selectively inhibits responses to sweet substances in rodents. The present study investigated possible interaction between gurmarin and the submandibular saliva in rats fed diet containing gymnema. Electrophoretic analyses demonstrated that relative amounts of two proteins in the saliva clearly increased in rats fed the gymnema diet. However, rats previously given section of the bilateral glossopharyngeal nerve showed no such salivary protein induction. Analyses of amino acid sequence indicate that two proteins are rat kallikrein 2 (rK2) and rat kallikrein 9 (rK9). rK2 and rK9, a family of serine proteases, have a striking resemblance of cleavage site in the protein substrates. Interestingly, gurmarin possesses comparable residues with those rK2 and rK9 prefer. The kallikreins significantly inhibited immunoreaction between gurmarin and antigurmarin antiserum. These results suggest that rK2 and rK9 increased by chemosensory information for the gymnema diet via the glossopharyngeal nerve might cleave gurmarin or at least cause specific binding with it.

Amino Acid Sequence↗
PubMed2006

Amiloride inhibition on NaCl responses of the chorda tympani nerve in two 129 substrains of mice, 129P3/J and 129X1/SvJ.

Amiloride, a sodium channel blocker, is known to suppress NaCl responses of the chorda tympani (CT) nerve in various mammalian species. In mice, the NaCl suppressing effect of amiloride is reported to differ among strains. In C57BL mice, amiloride inhibits NaCl responses to about 50% of control, whereas no such clear suppression was evident in prior studies with 129 mice. However, evidence from behavioral studies is not entirely consistent with this. Recently, it has been found that genetic backgrounds of 129 mice differ within substrains. 129X1/SvJ (formerly 129/SvJ) mice differ from the 129P3/J (formerly 129/J) strain by 25% of sequence length polymorphisms. Therefore, we examined possible substrain difference between 129P3/J and 129X1/SvJ mice in the amiloride sensitivity of electrophysiologically recorded NaCl responses. Amiloride significantly suppressed CT responses to NaCl without affecting responses to KCl both in 129P3/J and 129X1/SvJ mice. However, the magnitude of the amiloride inhibition was significantly larger (approximately 50% of control in response to 0.01-1.0 M NaCl by 100 microM amiloride) in 129X1/SvJ than in 129P3/J mice (approximately 20% of control in response to 0.03-0.3 M NaCl by 100 microM amiloride). Threshold amiloride concentration for suppression of responses to 0.3 M NaCl was 30 microM in 129P3/J mice, which was higher than that in 129X1/SvJ mice (10 microM). In 129X1/SvJ mice, the threshold amiloride concentration eliciting inhibition of NaCl responses and the magnitude of the inhibition were comparable with those in C57BL/6 mice. These results suggest that amiloride sensitivity of NaCl responses differs even among the 129 substrains, 129P3/J and 129 X1/SvJ, and the substrain difference of 129 mice in amiloride sensitivity is as large as that between two inbred strains (129P3/J and C57BL/6).

Amiloride↗
PubMed2006

Trpm5 null mice respond to bitter, sweet, and umami compounds.

Trpm5 is a calcium-activated cation channel expressed selectively in taste receptor cells. A previous study reported that mice with an internal deletion of Trpm5, lacking exons 15-19 encoding transmembrane segments 1-5, showed no taste-mediated responses to bitter, sweet, and umami compounds. We independently generated knockout mice null for Trpm5 protein expression due to deletion of Trpm5's promoter region and exons 1-4 (including the translation start site). We examined the taste-mediated responses of Trpm5 null mice and wild-type (WT) mice using three procedures: gustatory nerve recording [chorda tympani (CT) and glossopharyngeal (NG) nerves], initial lick responses, and 24-h two-bottle preference tests. With bitter compounds, the Trpm5 null mice showed reduced, but not abolished, avoidance (as indicated by licking responses and preference ratios higher than those of WT), a normal CT response, and a greatly diminished NG response. With sweet compounds, Trpm5 null mice showed no licking response, a diminished preference ratio, and absent or greatly reduced nerve responses. With umami compounds, Trpm5 null mice showed no licking response, a diminished preference ratio, a normal NG response, and a greatly diminished CT response. Our results demonstrate that the consequences of eliminating Trmp5 expression vary depending upon the taste quality and the lingual taste field examined. Thus, while Trpm5 is an important factor in many taste responses, its absence does not eliminate all taste responses. We conclude that Trpm5-dependent and Trpm5-independent pathways underlie bitter, sweet, and umami tastes.

Animals↗
PubMed2005

Heat activation of TRPM5 underlies thermal sensitivity of sweet taste.

TRPM5, a cation channel of the TRP superfamily, is highly expressed in taste buds of the tongue, where it has a key role in the perception of sweet, umami and bitter tastes. Activation of TRPM5 occurs downstream of the activation of G-protein-coupled taste receptors and is proposed to generate a depolarizing potential in the taste receptor cells. Factors that modulate TRPM5 activity are therefore expected to influence taste. Here we show that TRPM5 is a highly temperature-sensitive, heat-activated channel: inward TRPM5 currents increase steeply at temperatures between 15 and 35 degrees C. TRPM4, a close homologue of TRPM5, shows similar temperature sensitivity. Heat activation is due to a temperature-dependent shift of the activation curve, in analogy to other thermosensitive TRP channels. Moreover, we show that increasing temperature between 15 and 35 degrees C markedly enhances the gustatory nerve response to sweet compounds in wild-type but not in Trpm5 knockout mice. The strong temperature sensitivity of TRPM5 may underlie known effects of temperature on perceived taste in humans, including enhanced sweetness perception at high temperatures and 'thermal taste', the phenomenon whereby heating or cooling of the tongue evoke sensations of taste in the absence of tastants.

Animals↗
PubMed2005

Expression of amiloride-sensitive epithelial sodium channels in mouse taste cells after chorda tympani nerve crush.

Our previous electrophysiological study demonstrated that amiloride-sensitive (AS) and -insensitive (AI) components of NaCl responses recovered differentially after the mouse chorda tympani (CT) was crushed. AI responses reappeared earlier (at 3 weeks after the nerve crush) than did AS ones (at 4 weeks). This and other results suggested that two salt-responsive systems were differentially and independently reformed after nerve crush. To investigate the molecular mechanisms of formation of the salt responsive systems, we examined expression patterns of three subunits (alpha, beta and gamma) of the amiloride-sensitive epithelial Na(+) channel (ENaC) in mouse taste cells after CT nerve crush by using in situ hybridization (ISH) analysis. The results showed that all three ENaC subunits, as well as alpha-gustducin, a marker of differentiated taste cells, were expressed in a subset of taste bud cells from an early stage (1-2 weeks) after nerve crush, although these taste buds were smaller and fewer in number than for control mice. At 3 weeks, the mean number of each ENaC subunit and alpha-gustducin mRNA-positive cells per taste bud reached the control level. Also, the size of taste buds became similar to those of the control mice at this time. Our previous electrophysiological study demonstrated that at 2 weeks no significant response of the nerve to chemical stimuli was observed. Thus ENaC subunits appear to be expressed prior to the reappearance of AI and AS neural responses after CT nerve crush. These results support the view that differentiation of taste cells into AS or AI cells is initiated prior to synapse formation.

Amiloride↗
PubMed2005

Mouse strain differences in Gurmarin-sensitivity of sweet taste responses are not associated with polymorphisms of the sweet receptor gene, Tas1r3.

Gurmarin (Gur) is a peptide that selectively inhibits responses of the chorda tympani (CT) nerve to sweet compounds in rodents. In mice, the sweet-suppressing effect of Gur differs among strains. The inhibitory effect of Gur is clearly observed in C57BL/6 mice, but only slightly, if at all, in BALB/c mice. These two mouse strains possess different alleles of the sweet receptor gene, Sac (Tas1r3) (taster genotype for C57BL/6 and non-taster genotype for BALB/c mice), suggesting that polymorphisms in the gene may account for differential sensitivity to Gur. To investigate this possibility, we examined the effect of Gur in another Tas1r3 non-taster strain, 129 X 1/Sv mice. The results indicated that unlike non-taster BALB/c mice but similar to taster C57BL/6 mice, 129 X 1/Sv mice exhibited significant inhibition of CT responses to various sweet compounds by Gur. This suggests that the mouse strain difference in the Gur inhibition of sweet responses of the CT nerve may not be associated with polymorphisms of Tas1r3.

Animals↗
PubMed2005

Temporal changes in NCAM immunoreactivity during taste cell differentiation and cell lineage relationships in taste buds.

Neural cell adhesion molecule (NCAM) is a type III cell marker in the taste buds. In order to clarify the cell type of Mash1-expressing cells in taste buds, expression of NCAM was examined in Mash1-expressing taste cells of adult mice in comparison with gustducin- and T1r3-expressing cells, using a combination of NCAM immunohistochemistry and in situ hybridization. About 98% of Mash1-expressing cells were NCAM immunopositive (IP), suggesting that Mash1-expressing cells should be categorized as type III cells. Unexpectedly, small subsets of gustducin- and T1r3-expressing cells were also found to be NCAM-IP, contradicting previous immunohistochemical studies in rats, in which gustducin-IP cells were observed specifically in type II cells, which do not have NCAM immunoreactivity. Examinations of developing taste buds showed temporal changes in the ratio of NCAM-IP cells in gustducin- and T1r3-expressing cells; the ratio of NCAM-IP cells in these gene-expressing cells were approximately 90% at 0.5 days after birth and decreased markedly during development. In contrast, the majority of Mash1-expressing cells showed constant NCAM immunoreactivity throughout development. In addition, BrdU-labeling experiments showed that the differentiation of Mash1-expressing cells precedes those of gustducin- and T1r3-expressing cells in taste buds of adult mice. These results suggest that T1r3- and gustducin-expressing cells are NCAM-IP at the beginning of cell differentiation, and that NCAM immunoreactivity in gustducin- and T1r3-expressing cells might remain from the previous developmental stage expressing Mash1.

Animals↗
PubMed2004

Umami taste responses are mediated by alpha-transducin and alpha-gustducin.

The sense of taste comprises at least five distinct qualities: sweet, bitter, sour, salty, and umami, the taste of glutamate. For bitter, sweet, and umami compounds, taste signaling is initiated by binding of tastants to G-protein-coupled receptors in specialized epithelial cells located in the taste buds, leading to the activation of signal transduction cascades. Alpha-gustducin, a taste cell-expressed G-protein alpha subunit closely related to the alpha-transducins, is a key mediator of sweet and bitter tastes. Alpha-gustducin knock-out (KO) mice have greatly diminished, but not entirely abolished, responses to many bitter and sweet compounds. We set out to determine whether alpha-gustducin also mediates umami taste and whether rod alpha-transducin (alpha(t-rod)), which is also expressed in taste receptor cells, plays a role in any of the taste responses that remain in alpha-gustducin KO mice. Behavioral tests and taste nerve recordings of single and double KO mice lacking alpha-gustducin and/or alpha(t-rod) confirmed the involvement of alpha-gustducin in bitter (quinine and denatonium) and sweet (sucrose and SC45647) taste and demonstrated the involvement of alpha-gustducin in umami [monosodium glutamate (MSG), monopotassium glutamate (MPG), and inosine monophosphate (IMP)] taste as well. We found that alpha(t-rod) played no role in taste responses to the salty, bitter, and sweet compounds tested or to IMP but was involved in the umami taste of MSG and MPG. Umami detection involving alpha-gustducin and alpha(t-rod) occurs in anteriorly placed taste buds, however taste cells at the back of the tongue respond to umami compounds independently of these two G-protein subunits.

Animals↗
PubMed2004

A strong nerve dependence of sonic hedgehog expression in basal cells in mouse taste bud and an autonomous transcriptional control of genes in differentiated taste cells.

The nerve-dependency of gene expression in mouse taste bud was examined through an analysis of changes in gene expression in and around the taste buds in circumvallate papillae after surgery of cranial nerve IXth (glossopharyngeal nerve). The number of cells expressing T1r3, gustducin, Mash1 and Nkx2.2 gradually decreased after denervation. However, the expression intensity of these genes was barely influenced by denervation, and strong expression was observed at 6 days after denervation. In contrast, the basal cell-specific Sonic hedgehog (Shh) expression in the taste buds was decreased markedly at 6 h after denervation. In the regeneration process of taste buds, Shh expression was observed during a very early phase before taste bud formation. These results indicate the autonomous transcriptional control of genes in differentiated taste cells and the strong nerve-dependency of Shh expression in basal cells. Furthermore, in order to reveal the mitotic activity of Shh-expressing cells in taste buds, the BrdU-labeling experiments were performed using a combination of BrdU-immunohistochemistry and in situ hybridization. BrdU-signal was very rarely observed in Shh-expressing cells immediately after BrdU injection, and the signals were noted mainly in Ptc-expressing cells. BrdU signals rapidly increased in Shh-expressing cells in following 12 h and began to decrease after 2 days post-injection. These results suggest that most Shh-expressing cells are not mitotically active, but that Shh-expressing cells may be in the early transient developmental state of taste cells in taste buds.

Animals↗
PubMed2003

Regional expression patterns of taste receptors and gustducin in the mouse tongue.

In order to understand differences in taste sensitivities of taste bud cells between the anterior and posterior part of tongue, it is important to analyze the regional expression patterns of genes related to taste signal transduction on the tongue. Here we examined the expression pattern of a taste receptor family, the T1r family, and gustducin in circumvallate and fungiform papillae of the mouse tongue using double-labeled in situ hybridization. Each member of the T1r family was expressed in both circumvallate and fungiform papillae with some differences in their expression patterns. The most striking difference between fungiform and circumvallate papillae was observed in their co-expression patterns of T1r2, T1r3, and gustducin. T1r2-positive cells in fungiform papillae co-expressed T1r3 and gustducin, whereas T1r2 and T1r3 double-positive cells in circumvallate papillae merely expressed gustducin. These results suggested that in fungiform papillae, gustducin might play a role in the sweet taste signal transduction cascade mediated by a sweet receptor based on the T1r2 and T1r3 combination, in fungiform papillae.

Animals↗