The response elicited by any given taste is not determined by the taste itself. The animal's experience with the taste and its postingestive effects, and it's metabolic state when it encounters a taste are factos that contribute to responses to taste. The particular response elicited by a taste derives from the neural integration of these 3 factors. One of the principal aims of this proposal is to determine the sites within the caudal brainstem (CBS) that integrate taste and internal state. Our experiments with chronic decerebrate rats and fourth ventricular infusions in intact rats demonstrate that taste and metabolic state information is integrated within the CBS. Another aim of the proposed experiments is to determine the nature of the metabolic state feedback that is integrated with taste to affect behavior. A variety of techniques including: intronal infusion of a sucrose concentration series, vagal deafferentation, surgical interference with the digestive tract and pontine and medullary gustatory nucleus lesions are used for these purposes. The long term goal of these experiments is to define the capacity of several neural levels of the rat brain to modify ingestive consummatory responses as a function of physiological and experiential factors and in so doing to examine whether a hierarchical hypothesis of ingestive control will help decipher the organization of a motivated and regulated system such as energy homeostasis.
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