Recent advances have suggested a strong spatial component in the organization of olfactory receptor neurons (ORNs). Multineuron electroolfactogram (EOG) recordings spaced systematically across the rat olfactory epithelium show selective responses to odorants with certain chemical structures. The regions of the epithelium responding differently to polar and nonpolar odorants express different subgroups of olfactory receptor genes and ORNs of these regions send axons to different parts of the olfactory bulb. This suggests a spatial factor in olfactory processing. The behavior of individual ORN populations or of receptor protein populations has not been extensively surveyed, although a small number have been studied. We will use findings from our EOG recordings as a guide to investigate the properties of individual ORNs. The ultimate goal is to find principles by which chemical structure determines odor quality. For example, it is hypothesized that most ORNs in the dorsal epithelium will be more responsive to polar molecules, while those in the ventral epithelium will be more responsive to saturated hydrocarbons. Because of evidence suggesting diversity in receptor mechanisms, the possibility of inhibitory interactions in ORNs will be studied. The studies will be done in the intact rat olfactory epithelium to preserve both spatial relationships and the processes 'occurring in the surrounding tissue. The primary technique will be extracellular single unit recording, although intracellular penetrations may be used to validate conclusions about inhibitory actions or confirm that very broad response spectra result from ORNs rather than multicellular recordings. The research should provide a greater understanding of the spatial organization of inputs to the olfactory bulb. The data may ultimately aid in the understanding of the basic functioning of this sensory system, which is important in social and alimentary behaviors.
