In past studies in which we mapped 2-deoxyglucose uptake evoked by systematically different odorant chemicals across the entire rat olfactory bulb, glomerular responses could be related to each odorant's particular oxygen-containing functional group. In the present study we tested whether aliphatic odorants containing two such functional groups (esters, ketones, acids, alcohols, and ethers) would stimulate the combination of glomerular regions that are associated with each of the functional groups separately, or whether they would evoke unique responses in different regions of the bulb. We found that these very highly water-soluble molecules rarely evoked activity in the regions responding to the individual functional groups; instead, they activated posterior glomeruli located about halfway between the dorsal and ventral extremes in both the lateral and the medial aspects of the bulb. Additional highly water-soluble odorants, including very small molecules with single oxygenic groups, also strongly stimulated these posterior regions, resulting in a statistically significant correlation between posterior 2-deoxyglucose uptake and molecular properties associated with water solubility. By showing that highly water-soluble odorants stimulate a part of the bulb associated with peripheral and ventral regions of the epithelium, our results challenge a prevalent notion that such odorants would activate class I odorant receptors located in zone 1 of the olfactory epithelium, which projects to the dorsal aspect of the bulb.
(c) 2007 Wiley-Liss, Inc.