Psychophysical Evaluation of Taste Function

 描述（由申请人提供）：尽管复合碳水化合物和氨基酸在包括人类在内的杂食动物的饮食中很重要，但我们对味觉系统检测和处理这些关键饮食化合物的外周和中枢机制的理解仍处于起步阶段。自从T1 R受体蛋白家族的最初发现和表征以来，已经积累了支持T1 R2 +3异二聚体作为甜味配体的主要味觉受体的证据。同样，T1 R1 +3异二聚体被认为在存在5 '-核糖核苷酸肌苷一磷酸（IMP）时，在原型“鲜味”化合物L-谷氨酸的感知中是关键的。然而，与此同时，来自该实验室和其他实验室的研究表明，额外的，潜在的T1 R非依赖性受体可能参与至少一些氨基酸的存在，包括L-谷氨酸与IMP混合时的信号。这些结论部分基于T1 R1或T1 R3缺失的单基因敲除（KO）小鼠的残留行为和神经反应。类似地，缺乏T1 R2或T1 R3的小鼠，虽然对常见糖显示出严重受损的心理物理反应性，但对葡萄糖聚合物混合物如多糖的反应性仅轻度受损。在异二聚体的单个T1 R亚基缺失后保留的味觉功能可能是由于剩余的亚基形成同二聚体或与未鉴定的蛋白质联合收割机结合以充当部分有效受体的能力。或者，这种维持的功能可以反映T1 R独立的机制。因此，通过使用严格的心理物理学方法，在拟定研究中检测T1 R2 +3双KO和新生成的T1 R1 +3双KO小鼠沿着野生型（WT）小鼠，以确定T1 R非依赖性受体是否有助于葡萄糖聚合物溶液的可检测性，并选择氨基酸，如L-谷氨酸（+IMP）、甘氨酸和L-赖氨酸。神经横切研究将分离负责维持双KO小鼠对相关刺激的行为反应性的关键口服受体场。最后，因为在给定的味觉任务中任何行为能力的缺乏都可能不反映到达大脑的外周信号的缺乏，所以将在孤束吻侧核（rNST）中进行单单位记录，第一次中枢味觉中继，f WT和双KO小鼠。这将决定这些味觉刺激产生的信号是否到达大脑，以及它们来自哪个口腔区域。此外，将确定相关T1 R异二聚体受体的丢失是否差异地影响特定功能性神经元类型中的诱发活性，如通过响应曲线和解剖投影状态所定义的。这些综合的行为和电生理学研究不仅将揭示葡萄糖聚合物和选择氨基酸的T1 R独立味觉信号是否存在，而且将深入了解它们的神经通道及其功能意义。

 DESCRIPTION (provided by applicant): Despite the importance of complex carbohydrates and amino acids in the diet of omnivores including humans, our understanding of the peripheral and central mechanisms underlying the detection and processing of these critical dietary compounds by the gustatory system remains in its infancy. Since the initial discovery and characterization of the T1R family of receptor proteins, evidence has accumulated supporting the T1R2+3 heterodimer as the primary taste receptor for sweet-tasting ligands. Likewise, the T1R1+3 heterodimer has been suggested to be critical in the perception of the prototypical "umami" compound, L-glutamate, when in the presence of the 5'-ribonucleotide, inosine monophosphate (IMP). At the same time, however, research from this lab and others has suggested that additional, potentially T1R-independent receptors may be involved in signaling the presence of at least some amino acids, including L-glutamate when mixed with IMP. Such conclusions are based, in part, on residual behavioral and neural responsiveness in single knock-out (KO) mice missing either T1R1 or T1R3. Similarly, mice lacking either T1R2 or T1R3, while displaying severely impaired psychophysical responsiveness to common sugars are only mildly impaired in responsiveness to glucose polymer mixtures such as Polycose. The taste function spared following deletion of single T1R subunits of the heterodimers may be due to the ability of the remaining subunit to form a homodimer or combine with an unidentified protein to serve as a partially effective receptor. Alternatively, such maintained function could reflect T1R-independent mechanisms. Accordingly, with the use of rigorous psychophysical methodology, T1R2+3 double KO and newly generated T1R1+3 double KO mice along with wild type (WT) mice will tested in the proposed studies to determine whether T1R-independent receptors contribute to the detectability of glucose polymer solutions and select amino acids such as L-glutamate (+IMP), glycine, and L-lysine. Nerve transection studies will isolate the critical oral receptor field(s) responsible for the maintained behavioral responsiveness to the relevant stimuli in the double KO mice. Finally, because it is possible that any lack of behavioral competence in a given taste task does not reflect the absence of a peripheral signal reaching the brain, single-unit recording in the rostral nucleus of the solitary tract (rNST), the first central taste relay, f WT and double KO mice will be performed. This will determine whether signals generated from these taste stimuli reach the brain and from what oral field they originate. Moreover, whether the loss of the relevant T1R heterodimeric receptors differentially affects evoked activity in particulr functional neuronal types, as defined by response profile and anatomical projection status, will be determined. These integrated behavioral and electrophysiological studies will not only reveal whether T1R-independent taste signals for glucose polymers and select amino acids exist, but will provide insight into their neural channeling and their functional significance.