Jr. Stapleton et al., The taste of monosodium glutamate (MSG), L-aspartic acid, and N-methyl-D-aspartate (NMDA) in rats: Are NMDA receptors involved in MSG taste?, CHEM SENSE, 24(4), 1999, pp. 449-457
Monosodium glutamate (MSG) is believed to elicit a unique taste perception
known as umami. We have used conditioned taste aversion assays in rats to c
ompare taste responses elicited by the glutamate receptor agonists MSG, L-a
spartic acid (L-Asp), and N-methyl-D-aspartate (NMDA), and to determine if
these compounds share a common taste quality. This informa- tion could shed
new light upon the receptor mechanisms of glutamate taste transduction. Ta
ste aversions to either MSG, L-Asp or NMDA were produced by injecting rats
with LiCl after they had ingested one of these stimuli. Subsequently, rats
were tested to determine whether they would ingest any of the above compoun
ds. The results clearly show that a conditioned aversion to MSG generalized
to L-Asp in a dose-dependent manner. Conversely, rats conditioned to avoid
L-Asp also avoided MSG. Conditioned aversions to MSG or L-Asp generalized
to sucrose when amiloride was included in all solutions. Importantly, avers
ions to MSG or L-Asp did not generalize to NMDA, NaCl or KCI, and aversions
to NMDA did not generalize to MSG, L-Asp, sucrose or KCI. These data indic
ate that rats perceive MSG and L-Asp as similar tastes, whereas NM DA, NaCl
and KCI elicit other tastes. The results do not support a dominant role fo
r the NMDA subtype of glutamate receptors in taste transduction for MSC (i.
e. umami) in rats.