This proposal, a request for an ADAMHA Research Scientist Award (RSDA), represents a synthesis of research concerned with the neural mechanisms that underlie the sensory control of ingestive behavior. In large part, the short-term control of ingestive behavior is governed by sensory neural processes originating in the oral cavity and viscera. Gustatory stimuli offer a unique sensory probe of this system because easily specifiable chemical stimuli reliably elicit ingestion or rejection. Visceral afferent activity or hormone levels somehow modify the gustatory neural activity such that the behavioral response to the same chemical stimulus is switched from ingestion to rejection, or vice versa. This process, switching behavioral responses elicited by an external stimulus as a function of changing internal stimuli, contains the essential elements of biological motivation. In fact, ingestion is the common consummatory response for three drive systems, hunger, thirst, and salt appetite, that organize the behavioral components of energy, water, and electrolyte balance, respectively. This proposal outlines experiments that examine aspects of this response switching process using acute and chronic electrophysiological recording, experimental neuroanatomy, and behavioral techniques. The majority of the experiments focus on the caudal brainstem, particularly the medulla and pons. The caudal brainstem contains the first central synapses for both gustatory and vagal visceral afferent axons, the motoneurons responsible for ingestive behavior, and sufficient integrative capacity to support some behavioral manifestations of hunger and satiety. The specific objectives are (1) to examine the influence of duodenal nutrient infusions on brainstem gustatory activity, (2) to trace the interneuronal connections between oral sensory and oral motor neurons, (3) to test taste-guided behavior after disrupting the central gustatory system, (4) to compare the effects of need-free and deprivation-induced sodium appetite on gustatory processing, and (5) to search for evidence of convergence between central orosensory and olfactory activity. Conducting these experiments will provide an opportunity to learn, develop, or improve numerous techniques, including extracellular iontophoresis, chronic electrophysiology, animal psychophysical procedures and stimulus control, as well as to continue and expand collaborative arrangements with productive scientists elsewhere. In addition to contributing toward a basic understanding of how the nervous system coordinates sensory information into precise physiological and behavioral controls, this research has direct relevance to the etiology of specific behavioral pathology, such as dietary obesity, bulimia, and anorexia nervosa.
