Nakashima K, Katsukawa H, Sasamoto K, Ninomiya Y
Department of Chemistry, Asahi University School of Dentistry, Motosu-gun, Gifu, Japan.
J Nutr Sci Vitaminol (Tokyo). 2001 Apr;47(2):161-6. doi: 10.3177/jnsv.47.161.
Monosodium L-glutamate (MSG) and 5'-ribonucleotides elicit umami taste in humans and probably in some species of animals. Previous studies suggest that taste-mGluR4 and NMDA receptor may be involved in taste transduction for umami, but behavioral responses in rats do not support the involvement of NMDA receptor. In the present study, behavioral similarities and differences among MSG, mGluR4 agonist L(+)-2-amino-4-phosphonobutyrate (L-AP4), and NMDA receptor agonist N-methyl-D-aspartate (NMDA) were compared in C57BL mice by using a conditioned taste aversion paradigm. Mice conditioned to avoid either MSG or 10 mM L-AP4 appeared to avoid MSG, disodium 5'-inosinate (IMP), a mixture of MSG and IMP, and L-AP4, but not NMDA. Aversive conditioning to either sucrose or NMDA was generalized only to a mixture of MSG+IMP or NaCl. However, aversive conditioning to L-AP4 at 1 mM was generalized to NMDA and the umami substances. Lick rates for L-AP4 increased by mixing with (RS)-alpha-cycloprophy-4-phosphonophenylglycine (mGluR4 antagonist) when animals were conditioned to avoid MSG or L-AP4. Lick rates for NMDA also either decreased or increased by mixing with glycine (NMDA receptor coagonist) or D(-)-2-amino-5-phosphonopentanoic acid (NMDA receptor antagonist) when animals were conditioned to avoid L-AP4 or NMDA. In sucrose-conditioned mice. gurmarin (a sweet inhibiting peptide) suppressed the avoidance of sucrose and a mixture of MSG and IMP, but not L-AP4 and NMDA. The results suggest the possibility that to C 57BL mice MSG may taste similar to L-AP4 but different from NMDA, although both types of glutamate receptors as well as gurmarin-sensitive sweet receptor may be involved in perception of umami taste.
L-谷氨酸钠（MSG）和5'-核糖核苷酸能引起人类以及某些动物产生鲜味。先前的研究表明，味觉代谢型谷氨酸受体4（taste-mGluR4）和N-甲基-D-天冬氨酸受体（NMDA受体）可能参与鲜味的味觉转导，但大鼠的行为反应并不支持NMDA受体参与其中。在本研究中，通过使用条件性味觉厌恶范式，比较了C57BL小鼠对MSG、mGluR4激动剂L(+)-2-氨基-4-膦酰丁酸（L-AP4）和NMDA受体激动剂N-甲基-D-天冬氨酸（NMDA）的行为异同。经条件训练以避免摄入MSG或10 mM L-AP4的小鼠似乎会避免摄入MSG、5'-肌苷酸二钠（IMP）、MSG与IMP的混合物以及L-AP4，但不会避免摄入NMDA。对蔗糖或NMDA的厌恶条件反射仅会泛化至MSG + IMP或NaCl的混合物。然而，对1 mM L-AP4的厌恶条件反射会泛化至NMDA和鲜味物质。当动物经条件训练以避免摄入MSG或L-AP4时，L-AP4与（RS）-α-环丙基-4-膦酰苯甘氨酸（mGluR4拮抗剂）混合后舔舐率增加。当动物经条件训练以避免摄入L-AP4或NMDA时，NMDA与甘氨酸（NMDA受体共激动剂）或D(-)-2-氨基-5-膦酰戊酸（NMDA受体拮抗剂）混合后舔舐率也会降低或增加。在蔗糖条件训练的小鼠中，奇异果甜蛋白（一种甜味抑制肽）抑制了对蔗糖以及MSG与IMP混合物的回避，但不影响对L-AP4和NMDA的回避。结果表明，对于C57BL小鼠而言，尽管两种类型的谷氨酸受体以及对奇异果甜蛋白敏感的甜味受体可能都参与鲜味的感知，但MSG的味道可能与L-AP4相似，而与NMDA不同。
