Synaptic Processing in the Olfactory System

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Whether it be the aroma of our morning coffee or the scent of a lover, the sense of smell is a critical feature of daily life. The long-term objective of our research is to understand how olfactory information is processed in the mammalian brain. To address this question, we study the properties of neuronal circuits and synapses in the olfactory bulb and olfactory cortex, which are the first sites in the brain where olfactory information is processed. Our unifying hypothesis is that understanding the synaptic mechanisms of olfactory circuits is important for revealing how the brain encodes our sense of smell. The experiments proposed employ an in vitro brain slice preparation of the rat anterior piriform cortex. We also use a novel slice preparation in which the olfactory bulb remains attached to the cortex. Piriform cortex pyramidal cells and interneurons will be visualized using infrared differential interference optics. We will study these cells using whole-cell patch clamp recording and imaging of intracellular calcium concentration. Specific Aim 1 proposes to characterize the fundamental mechanisms governing the transfer of sensory information from the olfactory bulb to the cortex. We hypothesize that individual mitral cells can make strong connections onto piriform pyramidal cells and that the synaptic integration of relatively few mitral cell inputs underlies feature detection in piriform cortex. Specific Aim 2 proposes to investigate the role of local inhibitory circuits in shaping synaptic integration in piriform cortex. We hypothesize that feedforward and feedback inhibitory interneurons regulate synaptic integration and spike output during physiologically relevant patterns of olfactory bulb input. Specific Aim 3 proposesto investigate population coding using imaging of cell activity in olfactory bulb-piriform cortex slices. We hypothesize that temporal and spatial patterns of pyramidal cell activity can encode information regarding the timing and localization of olfactory input in the olfactory bulb.These experiments will provide new insight into the synaptic mechanisms underlying olfaction in the brain.