Physiological Analysis of the Olfactory Projections

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DESCRIPTION: (provided by applicant) One important issue in olfactory physiology is the principle by which olfactory information may be coded and analyzed. Candidate principles include: a spatial code, a temporal code, and a random access code with the access being based on the history of association. There is evidence of a spatial separation of response ton odorants with different chemical properties in the olfactory epithelium. The convergence of axonal projection from olfactory receptor neurons (ORNs) to olfactory bulb glomeruli further refines this spatial pattern. Temporal factors include a prominent 3 0-80 Hz olfactory bulb oscillatory activity that is modulated by the inhibitory circuits of the olfactory bulb. Models based on insects suggest that timing of spikes relative to this oscillation are significant in coding odorant identity. However, the generation of this timing is not well understood. This proposal suggests that there are delays generated by two important mechanisms. The peripheral mechanism for these delays is the lag in OR.N activation due to the time required for some odorants to overcome sorption onto the walls of the nasal cavity and/or the time required to diffuse through the mucus and reach receptors. These delays will differ according to chemical properties and odorant concentration. The central mechanism for delays is the time required for interaction along the tangential surface of the bulb and is represented in the phase lags of the oscillatory field potential across space. This research will track the spatial and temporal features of odorant responses with olfactory bulb field potential and single unit recordings. Single cell recordings will distinguish between the two major output cell types, mitral and tufted cells, which we have shown to be differentially involved in the local circuitry of the bulb. The data will be analyzed to determine the temporal constraints on lateral inhibitory interactions within the olfactory bulb. We will also explicitly test the possibility that the involvement of output cells in oscillatory responses to an odorant is the result of experience with that odorant. These results will be of importance for understanding the sense of smell.