AN ANALYSIS OF SYNAPTIC TRANSMISSION MECHANISM FROM TASTE RECEPTOR CELL TO GUSTATORY NERVE

免疫组织化学研究表明，味蕾中存在含有5-羟色胺的味觉受体细胞。在以前的研究中，我们使用全自动上皮组织灌流/取样器和高效液相色谱法，检测到舌上皮浆膜侧分泌的5-羟色胺，这是对反复向舌上皮粘膜侧施加盐或柠檬酸的反应。因此，我们尝试使用局部刺激程序和碳纤维电极来检测味蕾对味孔施加味觉刺激时分泌的5-羟色胺。然而，我们无法检测到任何单胺类物质。我们尝试用免疫组织化学方法检测几种亚型的谷氨酸受体分子在菌状乳头的味蕾中的定位。MGluR4是一种代谢型谷氨酸受体，在味蕾细胞中有表达，但在传入突触的味觉神经末梢中没有表达。与…结合使用根据更多的电生理数据，味蕾细胞中的mGluR4可能对鲜味的转导机制起抑制作用。这些结果表明，谷氨酸和单胺以外的物质介导了味觉感受器细胞向味觉神经的传递。因此，我们使用瓦状乳头(VP)/von Ebner腺体(VEG)复合体进行了生物测定，其中几个受体分子在腺泡细胞上表达。结果表明，苦味刺激可抑制腺泡细胞电压门控性钾电流，而酸刺激可诱导慢时程腺泡细胞的内向电流反应，提示味觉刺激的这些作用是由味蕾细胞释放的递质的旁分泌效应所致。这些发现还表明，苦刺激释放的递质与酸刺激释放的递质不同，这多种递质的受体分子表达在VEG的腺泡细胞上。较少

Immunohistochemical studies have demonstrated that taste receptor cells containing serotonin exist in taste buds. In the previous studies, we detected serotonin secreted from the serosal side of the lingual epithelium in response to the repeated application of NaCl or citric acid to the mucosal side of the lingual epithelium using full-automatical perfusion/sampling device for epithelial tissue and HPLC. Therefore, we attempted to detect serotonin secreted from a single taste bud in response to the application of taste stimuli to the taste pore using localized stimulation procedure and carbon fiber electrodes. However, we were unable to detect any monoamines. We attempted to immunohistochemically detect localization of several subtypes of glutamatergic receptor molecules in the taste buds of the fungiform papilla. One of the metabotropic glutamatergic receptors, mGluR4 was detected in the taste bud cells, but not in the gustatory nerve terminal of the afferent synapse. Taken together w … More ith electrophysiological data, mGluR4 in the taste bud cells possibly play an inhibitory role for transduction mechanism of umami. These results suggest mat substances other than glutamate and monoamines mediate the transmission from taste receptor cells to gustatory nerves. Therefore, we performed a bioassay using vallate papilla (VP)/von Ebner's gland (VEG) complex, where several receptor molecules are expressed on the acinar cells. The results indicated that localized bitter stimuli to the cleft of isolated vallate papilla suppressed voltage-gated K^+ currents of acinar cells, whereas sour stimuli induced inward current responses in acinar cells with slow time course, suggesting that these actions of taste stimuli are due to paracrine effect of transmitters released from taste bud cells. These findings also suggest that transmitter released by bitter stimulus is different from that by sour stimulus, and receptor molecules for these multiple transmitters were expressed on acinar cells of VEG. Less