. The objective of the proposed research is to determine the neural substrates in the rodent hindbrain through which gustatory stimuli guide 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 to determine palatable from unpalatable stimuli is complete in the caudal brainstorm. The discrimination of palatable from unpalatable is evident by normal ingestion and rejection responses to taste stimuli in decerebrate preparations. Neuroanatomical studies suggest that polysynaptic pathways from the gustatory region of the rostral nucleus of the solitary tract influence oromotor nuclei producing the consummatory components of ingestion and rejection. These pathways overlap with brainstem sites identified with the generation of mastication, licking and swallowing. A series of chronic recording experiments in the rodent hind brain will determine to what extent different regions of the medullary reticular formation are involved in taste elicited ingestion and rejection. Because the oromotor functions of licking, swallowing and rejection share a common oral musculature, many of the same interneurons under investigation are expected to be involved in multiple functions. The involvement of a given neuron in multiple functions will be assessed by correlating neural activity with electromyographic responses from a subset of muscles involved in diverse functions. Time series analyses, spike counts, event averaging and spike triggered averaging will all be used to assess the response properties of reticular formation neurons during specific components of ingestion and rejection. One fundamental question to be addressed is the identity of neurons associated with the oral phase of rejection, the "gape" response. Are these neurons associated with neurons generating a lick cycle, a swallow-cycle, respiratory neurons, or a unique set of neurons? A parallel series of neuroanatomical studies will use double labeling techniques to identify regions of the brainstem differentially involved in ingestion and rejection and to further determine their connectivity with the oromotor nuclei.