Many odorants are complex structures involving combinations of multiple functional groups and hydrocarbon elements. On straight-chained hydrocarbon backbones, distinct functional groups appear to be coded as distinct molecular features (23,29,30). Aspects of hydrocarbon structure also appear to represent distinct molecular features when the functional group remains constant (24,27,28,30). Are these features coded independently or are there interactions between the features?  

Carboxylic acids and high concentrations of ketones activate particular glomerular modules independently of hydrocarbon structure (24,32). However, most glomerular modules appear to respond only to particular combinations of functional group and hydrocarbon structure (32). For example, modules responding to methyl esters and alcohols on a straight-chained backbone do not respond to methyl esters or alcohols containing a cyclohexyl hydrocarbon structure (32). Interactions of functional groups with aromatic, branched, and both branched and double-bonded hydrocarbon structures also were observed (32). Finally, aromatic compounds appear to stimulate a glomerular module that previously had been associated specifically with the ketone functional group (32).  

Alcohol functional group on different hydrocarbon structure backgrounds.  

There also are interactions between functional groups and their positions within a molecule. Whereas positional isomers of ketones evoke nearly identical activity patterns, the activity patterns evoked by alcohols depend heavily on the position of the hydroxyl group within a straight-chained hydrocarbon backbone (31). Intermediate effects were observed for positional isomers of esters (31).  

Effects of substitution position on patterns of 2-DG uptake evoked by seven-carbon alcohols.