The objective of this research proposal is to determine the neural substrate in the rodent hindbrain through which gustatory stimuli guides ingestive behavior. Although the regulation of ingestive behavior is exceedingly complex, involving widespread regions of the central nervous system, the basic regulatory function of taste is complete in the caudal brainstem. Chronic electromyographic recording experiments have characterized the behaviors of ingestion and rejection to gustatory stimuli by determining the activation sequences of a subset of trigeminal, facial, ambiguous and hypoglossal muscles. Recording from hypoglossal neurons in parallel with the electromyography reveals differential responses of protruder motoneurons from retractor motoneurons to different gustatory stimuli during ingestion and rejection. The neural substrate mediating these oro-motor responses is polysynaptic and anatomical experiments have delineated regions in the brainstem reticular formation and nucleus of the solitary tract as candidate regions for coordinating and sequencing the complex synergies of ingestion and rejection. Using neurophysiological techniques in acute experiments, neurons in these regions will be tested for their sensitivities to intra-oral tactile, gustatory and proprioceptive stimuli and connectivity to oro-motor nuclei. The dynamic responses of interneurons will be tested during ingestion and rejection and compared to motoneuron responses in chronic experiments. Anatomical tracing studies will determine if protruder and retractor motoneurons that respond differentially to gustatory stimuli have different interneuron projections. Chronic disorders such as obesity, hypertension and anorexia nervosa are related to disordered ingestion. Understanding the neurological basis of this fundamental biological decision to ingest or reject will contribute to the eventual solution of these chronic debilitating disorders
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