Our lab seeks to understand the development, formation, and refinement of neural circuits within the olfactory system. Our current focus has been on the organizational maps of the olfactory system and in particular the circuitry of the odor column which connects these maps and is considered by many to be the basic functional unit of the olfactory bulb. An odor column is a vertically oriented translaminar structure that extend from the surface of the bulb to the granule cell layer and consists of a glomerulus together its associated output and modulatory components below. Studies have shown that the glomerular and intrabulbar maps of the olfactory bulb are in part organized by the expression of odorant receptors in the olfactory sensory neurons (OSNs) of the nasal epithelium (Wang et al., Cell, 1998, Belluscio et al., Nature, 2002). Thus, to study the process by which odorant receptors help guide the formation of the odor column circuitry we have developed a transgenic method to express specific odorant receptors throughout the olfactory epithelium (Nguyan et al., Cell, 2007). Our recent experiments in conjunction with the Ryba lab in NIDCR we have shown that broad early expression of a single odorant receptor in immature OSNs disrupts the glomerular map and results in distorted activity patterns throughout the olfactory bulb (Nguyan et al., J. Neurosci., 2010). It is still unclear what the consequences of this glomerular disruption are on the organization of the intrabulbar map. In a second set of studies conducted in collaboration with the Koretsky lab in NINDS we have successfully detected the activation and downstream signaling patterns elicited by individual odorants in live anesthetized mice using Manganese-Enhanced MRI (MEMRI). These experiments demonstrated that MEMRI can be used to image odorant-induced activity throughout the entire olfactory bulb at the resolution of a single glomerulus (Chueng et al., Neuroimage, 2009;2010). In addition, since MEMRI is essentially non-invasive we use it to re-image the same olfactory bulb circuitry multiple times to study changes associated with odorant induced activity. Together, these studies have not only revealed new information about the formation of olfactory circuitry but also helped to develop new molecular and functional imaging tools that will facilitate our future studies of olfactory plasticity within that circuitry.
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