PERIPHERAL GUSTATORY PROCESSING

University Of Connecticut Sch Of Med/Dnt, Farmington CT

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Abstract

Recent convergence of several lines of experimental evidence ranging from molecular biology to behavior has helped to expose some of the basic mechanisms of the gustatory system. Three integrated behavioral, neurophysiological and genetic studies are proposed on golden hamsters (Mesocricetus auratus) and laboratory mice aimed at delineating the functioning of their sweet (attracting) and bitter (avoiding) taste systems. (1) Studies of mixtures address the nature, specificity and component inhibition in peripheral mixture processing by testing the ability of hamsters to recognize components in sucrose-quinine, dulcin- quinine and sucrose-quinine-NaCI mixtures. With a quasi-natural conditioned taste aversion (CTA) paradigm, hamsters trained to avoid components, by pairing drinking with LiCI injection, are behaviorally tested on binary and ternary mixtures. Chorda tympani and glossopharyngeal nerve recordings are used to test the limits of peripheral stimulation and inhibition on behavior; and, for Na+-quinine suppression, stimulus, nerve, and neuron specificity. (2) A definition of a bitter taste quality for hamsters is sought with behavioral and neural assays of aversive stimuli with diverse chemical (e.g., ionic vs. non-ionic) and biological (e.g., exposure-enhanced potency) properties. (3) Studies of genetic variation in sweet and bitter taste domains in multiple inbred strains of golden hamsters and mice seek sources of intake variation with behavioral assays and nerve recordings. Unitary bitter and unitary sweet hypotheses are tested by measuring thresholds for CTA learning and generalizing to multiple stimuli in mice selected for genetic variation in taste preferences and avoidances. The mouse behavioral experiments compare all stimuli at equal CTA saliency to avoid confounding stimulus concentration and intensity. Interpretation of mouse data is greatly facilitated by recent advances in definition of gustatory molecular receptors. By comparing data from hamsters and mice, we hope to establish common features that can be used to describe essential taste phenomena. Understanding taste function is a prerequisite for redressing taste disorders that can lead to serious problems with nutrition and homeostasis. Also, elimination of taste disorders would improve the quality of life that depends on enjoyment of food and drink, a universal human need contributing much to human sociality.