The long-term goal of this project is to gain an understanding of the chemoreceptive process by (1) performing a comparative ultrastructural study of taste buds in the mouse, rat, rabbit, mudpuppy and channel catfish, Ictalarus punctatus, and (2) correlating structure and function in the lingual taste buds of the mouse and mudpuppy (Necturus maculosus). The specific aims for this project are: 1. MORPHOLOGY: What is the normal morphology of TBs and taste cells in several species commonly used for ultrastructural and electrophysiological studies on taste? How many distinct cell types exist in TBs? We will use standardized techniques and protocols to characterize TBs and taste cells in mice, rats, rabbits, mudpuppies and channel catfish. 2. SYNAPSES: What is the structure of synapses associated with taste cells in mice? Do all taste cell types have synapses onto the same type of sensory nerve fibers? Are all TB synapses similar, or do different cell types have structurally different synapses? Are all postsynaptic elements identical? Do some fibers contain immunocytochemically definable peptides? 3. STRUCTYRE/FUNCTION: Can the ultrastructural features of TB cells and synapses be correlated with their electrophysiological responses? 4. CELL RENEWAL: Do the different cell types observed in murine TBs (e.g., light cells, dark cells) represent separate cell lines that arise independently? Alternatively, are TB cell types merely representative of different stages of growth of a single cell line? The results from these studies will help to answer basic questions concerning the structure, classification, function and renewal of cells in the gustatory systems of vertebrates, as well as to increase our understanding of how the nervous system interacts with target organs. These results, based on normal tissue, will provide baseline data which will be of value for future studies involving dysgeusia resulting from either pathology or normal aging.