Behavioral Taste Similarities and Differences among Monosodium L-Glutamate and Glutamate Receptor Agonists in C57BL Mice

抄録

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 behav-ioral 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 condi-tioned 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 ei-ther sucrose or NMDA was generalized only to a mixture of MSG +IMP or NaCI. However, aversive conditioning to L-AP4 at 1 mM was generalized to NMDA and the umami sub-stances. Lick rates for L-AP4 increased by mixing with (RS)-a-cycloprophy-4-phospho-nophenylglycine (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 antago-nist) 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 mix-ture of MSG and IMP, but not L-AP4 and NMDA. The results suggest the possibility that to C5 7PL 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 per-ception of umami taste.