The neurobiological mechanism of olfactory recognition and processing poses a challenge because of the wide variety of substances recognized. In other sensory systems, e.g., somatosensor and visual systems, extensive information about the sensory processing is available. However, understanding of the olfactory system lags far behind, although it has been possible to locate the regions activated by a particular odor molecule in the olfactory bulb (OB). This was done with 2-deoxyglucose (2-DG) autoradiography studies in which only one measurement can be made on each animal. Recent fMRI studies of the rat olfactory bulb have opened the path for a bette understanding of the mechanism of odor recogniton and processing. Patterns of glomerular activation in the olfactory bulb have been observed for the two commonly studied odorants amyl acetate and propionate by fMRI. The observed maps are in excellent agreement with the previously observed maps in 2-DG autoradiography experiments and can be repeated reproducibly. Therefore, the fMRI method allows many repeated experiments in the same animal mapping the odor-induced activation in the entire olfactory bulb with high spatial and temporal resolution. The goal of the proposed experiments is to correlate the activations, observed by fMRI, of the olfactory bulb with specific stereochemical features of the odorant molecules. T achieve this, the sensitivity of the fMRI will be improved in order to provide better spatial an temporal measures of OB activation. Reproducibility will be improved by better control of animal physiological conditions. The activation maps obtained will be coregistered with the anatomical MRI image. Under these improved conditions it should be possible to obtain well-resolved activation of individual glomeruli, which will be correlated with specific stereochemical features of the odorant molecules. The understanding of the odor-induced responses in the olfactory bulb to different chemicals holds promise for the eventual preventio and treatment of chemosensory disorders.
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