Research in the past two decades has greatly advanced our understanding of the mechanisms by which olfactory neurons detect and transmit odor information. However, many fundamental questions remain to be answered. One of the serious impediments to our understanding of olfaction is inability to match olfactory receptors with their cognate ligands. In this study, we take advantages of the zebrafish model organism and unique features of the fish olfactory system to deorphanize zebrafish olfactory receptors. We aim at determining olfactory receptors responsible to olfactory sensation of biologically meaningful stimuli including amino acids, bile acids, nucleotides, amines, catecholamines, hormonal steroids and prostaglandins. We will determine whether a group of olfactory receptors sensitive to a class of odorants resides within the same olfactory receptor family and has close phylogenic relationship. We will perform detail structure-response relationship and concentration-response relationship analyses to determine sensitivity and specificity of the deorphanized olfactory receptors. In fish, morphological and molecular biological studies suggest that ciliated and microvillous neurorns express distinct families of olfactory receptor genes and separate signal transduction molecules. We will confirm experimentally for the first time that different families of olfactory receptors activate distinct signal transduction mechanisms by performing pharmacological characterization of receptor induced signal transduction mechanisms. Our research plan is feasible owing to recent advances of olfactory receptor expression in a heterologous system that allows fast and sensitive screening to identify cognate ligands of an olfactory receptor in a manageable time period. Our study will provide new insights into the overall organization of an olfactory system and advance future research on information process and perception of the olfactory system using the zebrafish model organism. The data will be valuable for vertebrate comparative studies from physiological and evolutional view points. Furthermore, our investigation on sensitivity and specificity of G- protein coupled receptors in a heterologous system and demonstration of receptor-dependent activation of G- protein coupled signaling provide new vehicles for future studies on insights of structural and molecular organization that define binding specificity and activation selectivity of G-protein coupled receptors. PUBLIC HEALTH RELEVANCE: We deorphanize and functionally characterize zebrafish olfactory receptors. Utilizing this popular vertebrate model organism allows us to reduce research difficulties. The outcomes would advance our future research on physiological process of olfactory sensation. The study is beneficial to public health since findings of mechanisms of olfaction could help us understanding some devastating diseases.