This proposal represents synthesis of my research on the neural mechanisms that underlie the sensory control of ingestive behavior. In the course of 25 years of research, I discovered the sensory functions of the pontine parabrachial nuclei, the primary source of taste and visceral afferent projections to the limbic system, and played a significant role in redirecting the field toward the brainstem by examining the behavioral capacities of chronic decerebrate rats. During this period, I have directed more than 25 postdoctoral students, a number of whom have gone on to establish their own distinguished careers. The logic underlying my approach can be summarized as follows. The short term control of ingestive behavior is governed largely by sensory neural processes originating in the oral cavity and viscera. The gustatory system offers 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 so that ingestion is switched to rejection, or vice-a-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 3 drive systems, hunger, thirst, and salt appetite, that organize the behavioral components of energy, water, and electrolyte balance, respectively. Most of the experiments in this proposal focus on the brainstem, because it 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 satiety.
The specific aims are (1) to test taste-guided behavior after disrupting the central gustatory system, (2) to examine the influence of conditioned taste aversions and duodenal nutrient infusions on brainstem gustatory activity, and (3) to compare the effects of need-free and deprivation-induced sodium appetite on peripheral and central gustatory processing. 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 relevance to the etiology of behavior.
