GUSTATORY AFFERENT ORGANIZATION IN THE SOLITARY NUCLEUS

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The objectives of the proposed experiments are to characterize the sensitivity and central representation of gustatory receptor subpopulations in the oral cavity. Neurophysiological studies of taste function, particularly in the central nervous system, have usually stimulated only one subpopulation of taste receptors, the fungiform papillae on the anterior tongue. In addition to the anterior tongue, however, taste receptors are present in the foliate and circumvallate papillae on the posterior tongue, on the buccal wall, in and around the nasoincisor ducts of the hard palate, and on the soft palate. The proposed experiments will use techniques recently developed in this laboratory to record from taste-responsive neurons in the brainstem, while independently stimulating all six groups of oral gustatory receptors. Neurons in the first central gustatory relay, the nucleus of the solitary tract (NST), will be studied in the first three experiments. Experiments One and Two are designed to determine the degree of convergence of responses from these distinct taste receptor groups onto single neurons, as well as the anatomical loci of responses arising from these receptor subpopulations. The chemical sensitivities of the different receptor subpopulations will also be examined, most notably those on the palate because the chemical sensitivity of these receptors has only begun to be characterized. The effects of simultaneously stimulating separate subpopulations of gustatory receptors will be elucidated in the third experiment. The final set of experiments will extend our investigation to neurons in the second central gustatory relay, the parabrachial nuclei (PBN). During normal feeding, all the gustatory receptors in the oral cavity may be stimulated simultaneously, or in rapid succession. We cannot properly decipher the code for gustatory quality or the mechanisms through which taste influences feeding behavior without understanding the sensory barrage that arises from the entire receptor surface. The gustatory system exerts powerful influences on ingestive behavior, as well as autonomic and endocrine responses involved in the maintenance of energy, water, and electrolyte balance. Gustatory stimuli also exemplify the important hedonic responses to foods and drink that contribute to inappropriate ingestion patterns and that exascerbate such chronic conditions as obesity and hypertension.