Blonde Ginger D, Spector Alan C
Department of Psychology and Program in Neuroscience, Florida State University, Tallahassee, FL, USA.
Chem Senses. 2017 Jun 1;42(5):393-404. doi: 10.1093/chemse/bjx015.
The heterodimeric T1R1 + T1R3 receptor is considered critical for normal signaling of L-glutamate and 5'-ribonucleotides in the oral cavity. However, some taste-guided responsiveness remains in mice lacking one subunit of the receptor, suggesting that other receptors are sufficient to support some behaviors. Here, mice lacking both receptor subunits (KO) and wild-type (WT, both n = 13) mice were tested in a battery of behavioral tests. Mice were trained and tested in gustometers with a concentration series of Maltrin-580, a maltodextrin, in a brief-access test (10-s trials) as a positive control. Similar tests followed with monosodium glutamate (MSG) with and without the ribonucleotide inosine 5'-monophosphate (IMP), but always in the presence of the epithelial sodium channel blocker amiloride (A). Brief-access tests were repeated following short-term (30-min) and long-term (48-h) exposures to MSG + A + IMP and were also conducted with sodium gluconate replacing MSG. Finally, progressive ratio tests were conducted with Maltrin-580 or MSG + A + IMP, to assess appetitive behavior while minimizing satiation. Overall, MSG generated little concentration-dependent responding in either food-restricted WT or KO mice, even in combination with IMP. However, KO mice licked less to the amino acid stimuli, a measure of consummatory behavior in the brief-access tests. In contrast, both groups initiated a similar number of trials and had a similar breakpoint in the progressive ratio task, both measures of appetitive (approach) behavior. Collectively, these results suggest that while the T1R1 + T1R3 receptor is necessary for consummatory responding to MSG (+IMP), other receptors are sufficient to maintain appetitive responding to this "umami" stimulus complex in food-restricted mice.
异二聚体T1R1 + T1R3受体被认为对口腔中L-谷氨酸和5'-核糖核苷酸的正常信号传导至关重要。然而，缺乏该受体一个亚基的小鼠仍保留一些味觉引导的反应能力，这表明其他受体足以支持某些行为。在此，对缺乏两个受体亚基的小鼠（KO）和野生型（WT，n均为13）小鼠进行了一系列行为测试。在味觉计中，用一系列浓度的麦芽糊精Maltrin-580对小鼠进行训练和测试，在短暂接触测试（10秒试验）中作为阳性对照。随后用添加和不添加5'-肌苷酸（IMP）的味精（MSG）进行类似测试，但始终存在上皮钠通道阻滞剂阿米洛利（A）。在短期（30分钟）和长期（48小时）暴露于MSG + A + IMP后重复短暂接触测试，并用葡萄糖酸钠替代MSG进行测试。最后，用Maltrin-580或MSG + A + IMP进行渐进比率测试，以评估食欲行为同时尽量减少饱腹感。总体而言，即使与IMP联合使用，MSG在食物受限的WT或KO小鼠中产生的浓度依赖性反应也很少。然而，在短暂接触测试中，KO小鼠对氨基酸刺激的舔舐次数较少，这是一种 consummatory行为的衡量指标。相比之下，两组在渐进比率任务中的试验次数相似，断点也相似，这两种都是食欲（接近）行为的衡量指标。总的来说，这些结果表明，虽然T1R1 + T1R3受体对于对MSG（+IMP）的 consummatory反应是必需的，但其他受体足以维持食物受限小鼠对这种“鲜味”刺激复合物的食欲反应。
