Thyroid Hormone Effects on the Peripheral Olfactory System

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Roberts, William M. IBN 94-10637 The ability to recognize familiar locations by their sights, sounds and smells is a common phenomenon. In salmon, who migrate great distances from fresh water streams to vast salt-water oceans, and ultimately, back to their home streams to reproduce, the ability to identify their home streams is crucial to species survival. But how is it that these fish recognize their home environments? One possible mechanism is the incorporation of familiar smells into memory which occurs during the parr smolt in salmon. During smolting, a physical transformation takes place as does a maturation of olfactory memory. Additionally, smolting is accompanied by a marked increase in thyroid hormone levels. Drs. Roberts and Takahashi will examine the role of thyroid hormones in the development of olfactory memory. Olfactory receptor cells born at the time of the parr smolt will be chemically marked and the effect of exogenous thyroid hormone treatment to enhance their survival will be determined. Moreover, structural changes in the olfactory bulb of the brain at smolting and modulation of those changes by thyroid hormones will be assessed. In addition to examination of the structural changes occurring in the brain at the time of smolting, functional changes in the sensitivity of the olfactory receptor cells to odorants will be examined. These studies have the potential to provide a breakthrough in understanding the physical basis of memory. Further, migration of salmon is of considerable commercial interest. This research has the potential to allow man to devise methods for guiding salmon to their birthplaces following novel pathways that may enhance the survival of the species.