CROSS-ADAPTATION OF SWEATY-SMELLING 3-METHYL-2-HEXENOIC ACID BY A STRUCTURALLY-SIMILAR, PLEASANT-SMELLING ODORANT

Cross-adaptation has been interpreted as a measure of the degree to wh ich odors share common sensory channels. How structural similarity, in the absence of perceptual similarity, influences cross-adaptation is unknown. The present study assessed cross-adaptation by structurally s imilar, but perceptually different, odorants. Magnitude estimates for a 10:1 mixture of (E) and (Z)-3-methyl-2-hexenoic acid (3M2H), a princ ipal component of human underarm odor, decreased following adaptation to a mixture of (E)- and (Z)-ethyl esters of 3M2H (EE3M2H), which poss ess a pleasant, fruity odor. Cross-adaptation was asymmetric; adaptati on to 3M2H did not significantly affect the perceived intensity of EE3 M2H. By contrast, there was no significant cross-adaptation between 3M 2H and the fruity-smelling ethyl esters of its homologues, 3-methyl-2- octenoic acid (EE3M20) and 3-methyl-2-pentenoic acid (EE3M2P). Similar ity ratings revealed no differences among the three ethyl esters in th eir perceptual similarity to 3M2H (i.e. all were rated equally dissimi lar to 3M2H). Molecular modeling studies revealed no difference in the charge distribution of these molecules. Rather, differences in the sh ape and size of the hydrophobic part of the molecule may determine the extent of cross-adaptation. These results demonstrate that structural ly-similar, yet perceptually-distinct, odorants may cross-adapt and su ggest that the extent of cross-adaptation may be affected by the degre e of structural, as well as perceptual, similarity.