PHYSIOLOGICAL ANALYSIS OF THE OLFACTORY PROJECTIONS

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Olfactory sensory coding at the olfactory bulb level is poorly understood, in spite of much new information on the anatomy and physiology of mammalian olfactory bulb local circuits. This laboratory has contributed to the information on local circuits and is now analyzing the odor responses of olfactory bulb cells in terms of local circuit interactions. The form of the neural response to odor is strongly influenced by the stimulus intensity, and it is necessary to systematically manipulate the stimulus intensity to determine whether cells can discriminate between different odors. In this work, appropriate controls of stimulus intensity will be used to study the neural response during changes in odor quality. The spatial interaction of afferents to each recorded cell will be tested by stimulation of the olfactory nerve layer. The work will test whether there are spatially organized excitatory and inhibitory influences for each recorded cell and relate these influences to the pattern of response to odor. Projection cells and interneurons will be identified by antidromic activation, by patterns of synaptic activation and by intracellular marking. An improved index of response magnitude will allow better evaluation of responses than has been possible in the past. Spatial organization of odor sensitivity at the mucosa and in the glomerular layer of the bulb is well established. The local circuits interactions of the several types of projection cells differ in ways that suggest varying sensitivity to this spatial organization. These cells also differ in their central projections. The proposed work will test the degree to which these relationships correlate with the odor quality and odor intensity responses of cells of the bulb. Olfaction is important in feeding, sexual and social behaviors in many species as well as in endocrine function. This research is significant for the understanding of odor quality and intensity coding. The potential for functionally separate central projections that may filter the sensory input in ways that are useful for specialized functions will be explored. Such specialized projection systems exist in the processing of other senses and these data may help lead to important generalizations about sensory function.