Neurophysiological, morphological, and behavioral studies are planned to learn how developing peripheral and central nervous system taste neurons are influenced by early environmental factors. Neurophysiological taste responses from single chorda tympani nerve fibers will be recorded in rats fed a NaCl-deficient diet during early development. The period of deprivation will extend from 3 days gestation to prepubertal ages or to adulthood. Therefore, the effects of the deprivation period on functional responses will be examined. Moreover, the """"""""plasticity"""""""" of the gustatory system will be studied by recording taste responses from rats initially deprived of dietary NaCl to prepubertal ages or to adulthood and then fed a NaCl-replete diet for 1 or 20 days. As a correlate to these neurophysiological experiments, the arborization patteRN of single chorda tympani fibers will be examined morphologically in the nucleus of the solitary tract (NST), the first central gustatory relay. In addition to these proposed studies, another series of experiments are planned to determine the critical period for central gustatory development. Specifically, studies are proposed to determine the developmental period when the NaCl-deficient diet alters neurophysiological taste responses in the NST, the terminal field organization of the chorda tympani nerve in the NST, and taste-guided behaviors. The proposed studies will provide new information on: 1) how response characteristics of single taste neurons are affected by prolonged periods of NaCl deprivation, 2) the extent to which neurophysiological taste responses in rats initially deprived of dietary NaCI appear to be normal after they are then fed a NaCl-replete diet, 3) how the arborization and projection patterns of single neurons are affected by early NaCl deprivation, 4) what the developmental endpoints are for the critical period in which early NaCl deprivation affects central gustatory system function and structure and affects taste guided behaviors, and 5) how the neurophysiological, morphological and behavioral critical periods relate to each other. The findings will provide new information on the development of peripheral and central nervous system taste responses, the neuroanatomical organization of the developing gustatory system, and on taste-guided behaviors that relate to the development of taste preferences and aversions and to the development of ingestive behaviors.
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