GENETICS OF CHEMOSENSORY RESPONSES TO SALTS AND ACIDS

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Little is known about the genetics of oral chemosensory responses to salts and acids, which often have a complex flavor and multiple mechanism of transduction. Chemosensory qualities representing different salts and acids include saltiness, sourness, bitterness, 'umami' and irritation. Therefore, sensitivity to each of these qualities may affect behavioral responses to salts and acids. In this study, we propose to compare acceptance of several salts [sodium, potassium and ammonium chloride, monosodium glutamate (MSG), inosine 5'-monophosphate (IMP)], acids (hydrochloric, citric and L-glutamic) and irritants (capsaicin and menthol) in thirty inbred mouse strains using 48-h-two-bottle preference tests. Two aspects will be analyzed; strain variation in the responses to individual compounds, and interrelationships among the strain responses to different compounds. Based on the strain variation, hypotheses of single- or multi-gene inheritance for individual compounds will be tested, which will provide a background for subsequent chromosomal mapping and eventually positional cloning of these genes. Co-variation and relatedness between responses to different salts and acids and responses to reference stimuli representing salty, sour, irritant (assessed in this project), bitter and sweet (known from literature) qualities will be assessed. Based on these relationships, patterns of the chemosensory qualities for each compound will be identified. The following questions will be examined: a) the role of genetic differences in bitter and salty taste sensitivity in ingestive responses to salts with a complex flavor (KCl, CaCl2, NH4Cl); b) the existence of a common factor that affects responses to MSG, IMP and glutamic acid, which could be attributed to 'umami' taste sensation; c) the role of genetic differences in salty, sour and sweet taste sensitivity in ingestive responses to 'umami' testing compounds (MSG, IMP, glutamic acid); d) the role of genetic differences in sensitivity to chemosensory irritation in ingestive responses to salts and acids at higher concentrations that evoke irritation. This study will further understanding of chemosensory perception of salts and acids, and will set the stage for future studies directed to identifying genes involved in the responses to salts and acids.