Olfactory receptor cells are specialized neurons that have many long tapering cilia, as in the main olfactory organ of mammal, or many long microvilli, as in the vomeronasal olfactory organ of mammals. The distal parts of these cilia and microvilli line the interface between the external odorous environment and the luminal surface of the olfactory epithelium. Their length and number results in a large surface area that presumably increases the chance that an odor molecule will encounter a receptor cell. The distal parts of cilia and microvilli are likely to contain molecules involved in olfactory signal-transduction, analogous to outer segments of rods and cones in the retina. This is the working hypothesis of this proposal. We previously found that putative components of the olfactory cilia. Further ultrastructural studies are needed to determine whether other presumed transduction components, such as odor receptors and the olfactory cyclic nucleotide gated channel, are also present in the distal parts of the olfactory cilia, and whether the transduction cascades present in cilia are also present in vomeronasal microvilli. The overall aim of the proposal is to address these questions. Olfactory signal-transduction is thought to begin when odor molecules interact with members of a large family of specific odor receptors. This interaction leads to activation of a special G-protein, Golf, which in turn stimulates type III adenylyl cyclase. The elevated level of cAMP that results leads to the opening of cyclic nucleotide-gated ion channels, thereby depolarizing the cell. There is also evidence for an additional olfactory signal transduction cascade that involves phospholipase C and inositol trisphosphate (IP3)-gated cation channels. Both transduction mechanisms could operate independently or, alternatively, act in concert with each other. It is not precisely known if individual olfactory neurons utilize both of these transduction cascades. While biochemistry, physiology, and light microscopy can indicate cells and, to some degree, subcellular regions, where certain processes take place, ultrastructural/immunocytochemical studies under optimal preservational conditions can allow finer analyses of structures such as cilia and microvilli.. Such studies will ascertain unambiguously whether the distal parts of these structures contain all of the molecules that have thus far been implicated in olfactory signal-transduction. We will apply such studies 1) to show whether components of adenylyl cyclase/cAMP and phospholipase C/1P3 signaling cascades are present in the same or different subcellular compartments in rat olfactory epithelium, 2) to analyze the location of odor receptors int eh rat olfactory epithelium to determine whether olfactory cilia do indeed contain odor receptors, a long held but still undocumented supposition, 3) to assess whether components of adenylyl cyclase/cAMP and/or phospholipase C/IP3 signaling cascades occur in rat vomeronasal epithelium and, if so, whether they are present in the same or different subcellular compartments.
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