Mechanisms of salty and bitter chemoreception in humans are not well understood, in part because compounds that block these tastes have not been available; and importantly, because animals models for salty and bitter taste perceptions are not fully applicable. Chlorhexidine glueonate, a bis-biguanide antiseptic, and weak cathodal electric currents greatly decrease salty and bitter tastes. Besides adaptation, no other experimental manipulations are known to have comparable effects in humans. Chlorhexidine is very bitter, but not salty. Chlorhexidine binds strongly to tissue, which may be related to its unique bis-eationic structure, giving it a long-lasting effect. Human psychophysical experiments are proposed? Cation/anion specificity of salty-bitter taste inhibition by 3 levels of ehlorhexidine and 2 levels of weak eathodal current is studied with experiments utilizing rating of taste intensity and taste-quality identification of equi-intense stimuli. Taste- stimulus identification is studied after treatment with two levels of ehlorhexidine with measures of information transferred (in bits). Tlo, a measure of consistency, is eomputed from a matrix of 10 replicate identifications of 10 stimuli. Forty-five Tes, measures of stimulus diseriminability, are eomputedfor all possible stimulus pairs. This """"""""confusion-matrix"""""""" methodology is an efficient and objective method for determining discriminability of multiple stimuli. Various salt and bitter stimulus combinations are included in sets of equi-intense stimuli to test the hypothesis that chlorhexidine affects ionic bitter stimuli more than non- ionic bitter stimuli. Two levels of chlorhexidine are used with concentration series of suerose, NaCI, citric acid and quinine.HC! to address the nature of the inhibition. Effects of adaptation to other bitter stimuli on the bitter taste of chlorhexidine are studied to establish whether one mechanism of action of chlorhexidine could involve its binding to a subset of bitter receptors. The experiments address the general hypothesis that transduction of salty stimuli is unitary, depending on ion-transport pathways; but bitter transduction is multiple, including ionic and non-ionic mechanisms. Greater understanding of gustatory perceptual processing in humans may lead to better management of taste disorders such as distressful salty-bitter dysgeusias and excessive salt intake.
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