Schier Lindsey A, Spector Alan C
Department of Psychology and Program in Neuroscience, Florida State University, Tallahassee, Florida 32306.
Department of Psychology and Program in Neuroscience, Florida State University, Tallahassee, Florida 32306
J Neurosci. 2016 Jan 6;36(1):113-24. doi: 10.1523/JNEUROSCI.3356-15.2016.
By conventional behavioral measures, rodents respond to natural sugars, such as glucose and fructose, as though they elicit an identical perceptual taste quality. Beyond that, the metabolic and sensory effects of these two sugars are quite different. Considering the capacity to immediately respond to the more metabolically expedient sugar, glucose, would seem advantageous for energy intake, the present experiment assessed whether experience consuming these two sugars would modify taste-guided ingestive responses to their yet unknown distinguishing orosensory properties. One group (GvF) had randomized access to three concentrations of glucose and fructose (0.316, 0.56, 1.1 m) in separate 30-min single access training sessions, whereas control groups received equivalent exposure to the three glucose or fructose concentrations only, or remained sugar naive. Comparison of the microstructural licking patterns for the two sugars revealed that GvF responded more positively to glucose (increased total intake, increased burst size, decreased number of pauses), relative to fructose, across training. As training progressed, GvF rats began to respond more positively to glucose in the first minute of the session when intake is principally taste-driven. During post-training brief-access taste tests, GvF rats licked more for glucose than for fructose, whereas the other training groups did not respond differentially to the two sugars. Additional brief access testing showed that this did not generalize to Na-saccharin or galactose. Thus, in addition to eliciting a common taste signal, glucose and fructose produce distinct signals that are apparently rendered behaviorally relevant and hedonically distinct through experience. The taste pathway(s) underlying this remain to be identified.
The T1R2+T1R3 heterodimer is thought by many to be the only taste receptor for sugars. Although most sugars have been conventionally shown to correspondingly produce a unitary taste percept (sweet), there is reason to question this model. Here, we demonstrate that rats that repeatedly consumed two metabolically distinct sugars (glucose and fructose), and thus have had the opportunity to associate the tastes of these sugars with their differential postoral consequences, initially respond identically to the orosensory properties of the two sugars but eventually respond more positively to glucose. Thus, in addition to the previously identified common taste pathway, glucose and fructose must engage distinct orosensory pathways, the underlying molecular and neural mechanisms of which now await discovery.
通过传统行为测量方法，啮齿动物对天然糖类（如葡萄糖和果糖）的反应，就好像它们引发相同的味觉感知质量。除此之外，这两种糖的代谢和感官效应有很大不同。考虑到对代谢上更便利的糖——葡萄糖——立即做出反应的能力，似乎有利于能量摄入，本实验评估了摄取这两种糖的经历是否会改变味觉引导的摄食反应，以适应它们尚不为人知的独特口部感官特性。一组（葡萄糖与果糖组，GvF）在单独的30分钟单次摄取训练时段中，随机获取三种浓度的葡萄糖和果糖（0.316、0.56、1.1 m），而对照组仅接受等量的三种葡萄糖或果糖浓度的暴露，或一直未接触糖。对两种糖的微观舔舐模式的比较显示，在整个训练过程中，相对于果糖，GvF组对葡萄糖的反应更积极（总摄入量增加、舔舐爆发大小增加、停顿次数减少）。随着训练的进行，GvF大鼠在训练时段的第一分钟，即摄入量主要由味觉驱动时，开始对葡萄糖有更积极的反应。在训练后的短暂摄取味觉测试中，GvF大鼠对葡萄糖的舔舐比对果糖更多，而其他训练组对这两种糖没有差异反应。额外的短暂摄取测试表明，这种情况不会推广到糖精钠或半乳糖。因此，除了引发共同的味觉信号外，葡萄糖和果糖还产生明显不同的信号，这些信号显然通过经历在行为上变得相关且在享乐方面有所不同。其背后的味觉通路仍有待确定。
许多人认为T1R2 + T1R3异二聚体是糖类的唯一味觉受体。尽管传统上大多数糖类已被证明相应地产生单一的味觉感知（甜味），但有理由质疑这一模型。在这里，我们证明，反复摄取两种代谢不同的糖（葡萄糖和果糖），从而有机会将这些糖的味道与其不同的口腔后效应联系起来的大鼠，最初对两种糖的口部感官特性反应相同，但最终对葡萄糖反应更积极。因此，除了先前确定的共同味觉通路外，葡萄糖和果糖必定涉及不同的口部感官通路，其潜在的分子和神经机制目前有待发现。
