Taste function

Abstract: Assessment of gustatory sensitivity in a clinical setting is the prerequisite for correct diagnosis and adequate treatment of taste dysfunction. Despite of this, no taste test has been established for the routine clinical testing. The aim of the present study was to create a protocol which is easy to administer. The presently used technique is based on strips made from filter paper which were impregnated with different taste solutions (four concentrations each for sweet, sour, salty and bitter). These strips are placed on the tongue and subjects are asked to identify the taste quality. After establishing the concentration range of the taste solutions, the test was tried in 69 subjects. Each subject received eighteen taste strips (four concentrations of each taste quality plus two blanks) in a pseudo-randomized sequence. Results from this new procedure correlated significantly with the results of the well established extensive three-drop-technique (r69 = 0.67). Repeated measures indicated good reproducibility of the results for the taste strips (r69 = 0.68). These data suggest the usefulness of this new technique in routine clinical practice. Major advantages are long shelf-life, convenience of administration, short time needed for testing (approximately 8 min), and the possibility to test each side of the tongue separately.

Abstract: In many sensory systems, stimulus sensitivity is dynamically modulated through mechanisms of peripheral adaptation, efferent input, or hormonal action. In this way, responses to sensory stimuli can be optimized in the context of both the environment and the physiological state of the animal. Although the gustatory system critically influences food preference, food intake and metabolic homeostasis, the mechanisms for modulating taste sensitivity are poorly understood. In this study, we report that glucagon-like peptide-1 (GLP-1) signaling in taste buds modulates taste sensitivity in behaving mice. We find that GLP-1 is produced in two distinct subsets of mammalian taste cells, while the GLP-1 receptor is expressed on adjacent intragemmal afferent nerve fibers. GLP-1 receptor knockout mice show dramatically reduced taste responses to sweeteners in behavioral assays, indicating that GLP-1 signaling normally acts to maintain or enhance sweet taste sensitivity. A modest increase in citric acid taste sensitivity in these knockout mice suggests GLP-1 signaling may modulate sour taste, as well. Together, these findings suggest a novel paracrine mechanism for the regulation of taste function.