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The Journal of Neuroscience, October 17, 2007, 27(42):11242-11253; doi:10.1523/JNEUROSCI.1227-07.2007
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Behavioral/Systems/Cognitive
Behavioral Discrimination between Sucrose and Other Natural Sweeteners in Mice: Implications for the Neural Coding of T1R Ligands
Cedrick D. Dotson andAlan C. Spector Department of Psychology and Center for Smell and Taste, University of Florida, Gainesville, Florida 32611-2250
Correspondence should be addressed to Cedrick D. Dotson at his present address: Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD 21201. Email: cdots003{at}umaryland.edu
In taste bud cells, two different T1R heteromeric taste receptors mediate signal transduction of sugars (the canonical "sweet" taste receptor, T1R2 + T1R3) and L-amino acids (the T1R1 + T1R3 receptor). The T1R1 + T1R3 receptor is thought to mediate what is considered the fifth basic taste quality "umami." However, a subset of L-amino acids is "sweet tasting" to humans and appears to possess a "sucrose-like" taste quality to nonhuman mammals. This suggests, to varying degrees, that all of these compounds activate a single neural channel that leads to the perception of sweetness.
The experiments detailed here were designed to test the ability of mice to distinguish between sucrose and various others sugars and L-amino acids in operant taste discrimination tasks. Mice had at least some difficulty discriminating sucrose from L-serine, L-threonine, maltose, fructose, and glucose. For example, when concentration effects are taken into consideration, mice discriminated poorly, if at all, sucrose from glucose or fructose and, to a lesser extent maltose, suggesting that sugars generate a unitary perceptual quality. However, mice were able to reliably discriminate sucrose from L-serine and L-threonine. Data gathered using a conditioned taste aversion assay also suggest that, although qualitatively similar to the taste of sucrose, L-serine and L-threonine generate distinctive percepts.
In conclusion, it appears that some signals from taste receptor proteins binding with sugars and some L-amino acids converge somewhere along the gustatory neuraxis. However, the results of these experiments also imply that sweet-tasting L-amino acids may possess qualitative taste characteristics that are distinguishable from the prototypical sweetener sucrose.
Key words: taste; sweeteners; mice; perception; coding; behavior
Received March 19, 2007; revised Aug. 30, 2007; accepted Sept. 1, 2007.
Correspondence should be addressed to Cedrick D. Dotson at his present address: Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD 21201. Email: cdots003{at}umaryland.edu
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