Olivia L. May, Ph.D. - US grants

[unreadable] DESCRIPTION (provided by applicant): The primary afferent terminations of the gustatory nerves are located in the nucleus of the solitary tract (NTS). These terminal fields extend in a rostral to caudal direction and are anatomically arranged in a dorsal to ventral fashion with distinct regions of overlap. Both the chorda tympani and glossopharyngeal fields have been identified as regions undergoing considerable plasticity in response to restriction of dietary sodium during development. Sodium deprivation results in expansion of both fields into the territory of adjacent fields increasing the proportion of overlap occurring among the respective fields. We hypothesize that the changes in terminal field morphology induced by dietary sodium restriction are a reflection of changes to the gustatory circuitry of the NTS. In order to elucidate changes occurring between pre- and post synaptic contacts between afferent terminations and NTS relay neurons, the following has been proposed: First, the circuitry between afferent terminal fields and gustatory relay neurons will be viewed using light microscopy and multiple fluorescent labeling techniques in order to elucidate the arrangement of NTS neurons among the gustatory fields and identify differences in terminal field/relay neuron interaction with respect to changes in dietary sodium content. Then, the synaptic morphology of the area will be characterized via electron microscopy, focusing specifically on differences between adult and sodium restricted animals that may correlate with alterations in terminal field formation. The results of these studies will further illuminate the general circuitry of the three gustatory terminal fields as well as provide insight, to the plasticity induced by a low sodium diet. [unreadable] [unreadable]

[unreadable] DESCRIPTION (provided by applicant): Afferent projections of trigeminal, facial, and glossopharyngeal nerves, which innervate lingual taste papillae, enter the hindbrain via the solitary tract and terminate in the solitary nucleus in a topography that reflects peripheral organization. How and when these sensory afferents are initially organized in the solitary tract are not well understood. Given the importance of an organized taste system for proper function, the long-term objective is to determine how the solitary tract is established. The scope of the proposed research aims to determine the developmental time course and distribution of sensory afferents comprising the solitary tract and to localize glia in relation to this development. To accomplish this, combinations of sensory ganglia will be labeled and solitary tract projections will be visualized in three dimension at a series of embryonic stages. Astrocytic glia will be immunohistochemically identified across developmental stages and correlated with solitary tract development for a role as a potential guidance factor. The working hypothesis is that taste and tongue nerve projections initially are separate from each other and gradually acquire extensive overlap within the solitary tract. Tract tracing via carbocyanine dyes and immunohistochemistry will be used to examine the organization of the solitary tract and to identify the relative location of astrocytes. The results of these experiments will provide a simultaneous, physical representation of the association of sensory afferents within the solitary tract and will demonstrate a possible cellular, astrocytic contribution to the organization of these afferents within the solitary tract. Potentially, the initial organization of sensory afferent projections in the solitary tract dictates the eventual organization of the associated terminal fields in the solitary nucleus. Therefore, these results will provide an important foundation for understanding the establishment of the primary afferent relay of the gustatory system. Taste sensation, which guides nutritive choices and ingestive behaviors of all vertebrates, is transduced by peripheral receptors and conveyed directly through the solitary tract to the medulla where it is integrated with other sensory inputs. Thus, a thorough knowledge of the organization of afferent projections within the solitary tract will contribute to a more complete understanding of how taste information is integrated in the central nervous system to inform diet choices, a behavior essential to sustain life. [unreadable] [unreadable] [unreadable]