Glutamate Taste: Discrimination between the Tastes of Glutamate Agonists and Monosodium Glutamate in Rats

• Published in: Chemical senses Vol. 29; no. 4; pp. 291 - 299
• Main Authors: Delay, E.R., Sewczak, G.M., Stapleton, J.R., Roper, S.D.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.05.2004; Oxford Publishing Limited (England)
• Subjects: amiloride; Amiloride - pharmacology; Aminobutyrates - pharmacology; Animals; aspartic acid; Aspartic Acid - pharmacology; Avoidance Learning; Biological and medical sciences; Discrimination (Psychology) - physiology; Excitatory Amino Acid Agonists - pharmacology; Fundamental and applied biological sciences. Psychology; L-AP4; Male; monosodium glutamate; N-Methylaspartate - pharmacology; NMDA; Olfactory system and olfaction. Gustatory system and gustation; Rats; Sodium Glutamate - pharmacology; Taste - physiology; taste discrimination; Taste Threshold; taste thresholds; Vertebrates: nervous system and sense organs; Differential threshold; Perception threshold; Rodentia; Rattus norvegicus; Psychophysics; Glutamate; Alimentary aversion; Vertebrata; Mammalia; Gustation; Detection threshold; Excitatory aminoacid; Neurotransmitter; NMDA; Perception; Taste
• ISSN: 0379-864X; 1464-3553; 1464-3553
• DOI: 10.1093/chemse/bjh031

Taste aversion studies have demonstrated that rats conditioned to avoid monosodium glutamate (MSG) with amiloride added to reduce the intensity of the sodium component of MSG taste, generalize this aversion to aspartic acid and to L-AP4, but not to ionotropic glutamate receptor agonists. That is, MSG, L-AP4 and aspartate have similar tastes to rats. However, conditioned taste aversion methods are unable to show to what extent the tastes of two substances are different. If two substances activate the same afferent processes (e.g. taste receptors), they are likely to produce the same tastes, but if they activate different afferent processes, the subject may detect differences between the tastes of the substances. In this study, rats were tested to determine if they could discriminate between the tastes of these agonists and MSG. We also established the detection thresholds for NMDA, aspartic acid and L-AP4, with and without amiloride (a sodium channel antagonist). Taste threshold values were 1–4 mM for NMDA and aspartic acid and 0.5–2.5 µM for L-AP4. None were affected by 30 µM amiloride. Rats could readily distinguish between the tastes of MSG and NMDA but they had difficulty discriminating between the tastes of aspartic acid and MSG. Rats could also easily distinguish between 10–100 mM MSG and 0.01–5 mM L-AP4. However, in two separate experiments error rates increased significantly when L-AP4 concentrations were between 10–100 mM, indicating that the tastes of L-AP4 and MSG were similar at these concentrations.