Caicedo A, Jafri M S, Roper S D
Department of Physiology and Biophysics and Program in Neuroscience, University of Miami School of Medicine, Miami, Florida 33136, USA.
J Neurosci. 2000 Nov 1;20(21):7978-85. doi: 10.1523/JNEUROSCI.20-21-07978.2000.
The neurotransmitters at synapses in taste buds are not yet known with confidence. Here we report a new calcium-imaging technique for taste buds that allowed us to test for the presence of glutamate receptors (GluRs) in living isolated tissue preparations. Taste cells of rat foliate papillae were loaded with calcium green dextran (CaGD). Lingual slices containing CaGD-labeled taste cells were imaged with a scanning confocal microscope and superfused with glutamate (30 micromter to 1 mm), kainate (30 and 100 micrometer), AMPA (30 and 100 micrometer), or NMDA (100 micrometer). Responses were observed in 26% of the cells that were tested with 300 micrometer glutamate. Responses to glutamate were localized to the basal processes and cell bodies, which are synaptic regions of taste cells. Glutamate responses were dose-dependent and were induced by concentrations as low as 30 microm. The non-NMDA receptor antagonists CNQX and GYKI 52466 reversibly blocked responses to glutamate. Kainate, but not AMPA, also elicited Ca(2+) responses. NMDA stimulated increases in Ca(2+) when the bath medium was modified to optimize for NMDA receptor activation. The subset of cells that responded to glutamate was either NMDA-unresponsive (54%) or NMDA-responsive (46%), suggesting that there are presumably two populations of glutamate-sensitive taste cells-one with NMDA receptors and the other without NMDA receptors. The function of GluRs in taste buds is not yet known, but the data suggest that glutamate is a neurotransmitter there. GluRs in taste cells might be presynaptic autoreceptors or postsynaptic receptors at afferent or efferent synapses.
味蕾中突触处的神经递质目前尚无确切定论。在此，我们报告一种用于味蕾的新型钙成像技术，该技术使我们能够在活的离体组织标本中检测谷氨酸受体（GluRs）的存在。用钙绿葡聚糖（CaGD）加载大鼠叶状乳头的味觉细胞。含有CaGD标记味觉细胞的舌切片用扫描共聚焦显微镜成像，并用谷氨酸（30微米至1毫米）、海人酸（30和100微米）、AMPA（30和100微米）或NMDA（100微米）进行灌流。在用300微米谷氨酸测试的细胞中，26%观察到了反应。对谷氨酸的反应定位于味觉细胞的突触区域，即基底突起和细胞体。谷氨酸反应呈剂量依赖性，低至30微米的浓度即可诱导。非NMDA受体拮抗剂CNQX和GYKI 52466可可逆地阻断对谷氨酸的反应。海人酸也能引发Ca(2+)反应，但AMPA不能。当对浴液进行改良以优化NMDA受体激活时，NMDA刺激细胞内[Ca(2+)]增加。对谷氨酸有反应的细胞亚群要么对NMDA无反应（54%），要么对NMDA有反应（46%），这表明可能存在两类对谷氨酸敏感的味觉细胞——一类有NMDA受体，另一类没有NMDA受体。味蕾中GluRs的功能尚不清楚，但数据表明谷氨酸在那里是一种神经递质。味觉细胞中的GluRs可能是传入或传出突触处的突触前自身受体或突触后受体。
