Project 3 involves a pilot study to directly investigate the diffusion of odorants in olfactory mucus using the salamander as the model system. Our present understanding of odorant diffusion and molecular transport in mucus is primarily based on electrophysiological measures and mathematical models, which may not accurately describe this initial process in olfaction. We propose to directly measure the diffusion coefficients of odorants in olfactory mucus using high-speed electrochemical recordings coupled with ejection of odorants by pressure-ejection from micropipettes. These electrochemical measurements are performed using microchemical sensors (30 microns in diameter) that are capable of directly measuring the diffusion of odorants and test species on time scales as rapid as 200 times per second (200 Hz). First, we plan to screen the electrochemical properties of odorants and determine their solution diffusion coefficients. These studies will lay the theoretical foundation for direct measures in mucus. Secondly, using the electrochemical recording techniques coupled with pressure ejection of chemicals from micropipettes, the apparent diffusion coefficients of odorants (vanillin,safrole) and test species (dopamine, ascorbic acid) will be measured in the olfactory mucus of three salamander species: Tiger Ambystoma tigtinum, Marbled Ambystoma opacum, and Spotted Ambystoma maculatum. Finally, when such measurements are perfected, we will attempt to measure the actual diffusion of an airborne odorant into and across the mucus layer. These studies should lead to a better description of the temporal dynamics of processes that precede olfaction.
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