The extent to which both innate and environmental factors influence early postnatal development of central gustatory neurons, and subsequent expression of taste-guided behaviors in adulthood, is poorly understood. Our studies have confirmed that elimination of normal gustatory afference to central gustatory neurons via unilateral superficial cauterizations of the anterior tongue retards normal development of the first-order central gustatory relay located in the rostral nucleus of the solitary tract (NST). Proposed experiments provide detailed information concerning the effects of early postnatal receptor damage on pre- and postsynaptic development of the rostral gustatory NST, and determine critical periods for receptor damage effects. Experiments also evaluate whether early receptor damage, and consequent alteration of neural development in the NST, affects the normal expression of taste-guided behaviors in adulthood. Transganglionic transport experiments using horseradish peroxidase are performed to evaluate volumetric differences in chorda tympani nerve (CT) terminal fields following early postnatal lingual receptor damage. Critical periods for NST development are examined in relation to the age at which receptor damage produces alterations in the normal development of CT fields. Golgi impregnation studies are conducted to describe the morphology of dendrites in the CT terminal field following lingual receptor damage, and immunohistochemical studies are performed to examine development of protein P-38, a specific integral membrane glycoprotein of clear presynaptic vesicles. Thus, development of both pre- and postsynaptic constituents of CT terminal fields are evaluated following damage produced during critical periods of NST development. Data derived from these studies will be compared to our existing data concerning normal neurological development of the rostral gustatory NST. Further information concerning the functional consequences of early receptor damage is obtained from behavioral studies that evaluate whether or not early receptor damage alters normal preferences and aversions to the four basic tastes in adulthood. Knowledge concerning the influence of anterior tongue stimulation on the development of central gustatory neurons during critical periods of early brain development is required to understand both the normal expression of taste-guided behaviors, and taste disorders which may be manifested because of gustatory deprivation produced by inadequate diet, early lingual receptor insult, or disease processes.
