CROSS-ADAPTATION BY STRUCTURAL ANALOGS 373 ratings (ten 3M2H, ten ME3M2H) during the five-minute adaptation period. Following these ratings, the adapting stimulus was removed and subjects continued to rate test stimuli every 15 seconds during a five-minute post-adaptation period. Subjects thus made a total of 20 ratings during this recovery period. In the second session, the adapting odorant, either 3M2H or ME3M2H, was reversed and the procedure repeated. The adapting odorant used in a particular session was counterbalanced across sessions for all subjects. Each magnitude estimate was converted to a percentage of the initial magnitude esti- mate for that odorant the resulting percentages are presented in Figure 2. These data were analyzed by a series of repeated, single-factor ANOVAs a separate analysis was performed for each comparison. The ANOVAs were calculated after each estimate was first subtracted from 100, allowing an assessment of whether estimates were signifi- cantly different from the initial estimates (100%). RESULTS Both 3M2H and ME3M2H showed significant self-adaptation (Table I). The pattern of self-adaptation observed was consistent with a pattern we have observed previously (3,10) strong self-adaptation occurred quickly and continued for the duration of the adaptation period. Following removal of the adapting odorant, each self-adapted odorant displayed a pattern of recovery to baseline levels (Table I). Significant cross-adaptation between 3M2H and ME3M2H was observed asymmetri- cally. Exposure to ME3M2H significantly reduced the perception of 3M2H via cross- adaptation, but there was no effect of 3M2H exposure on the perception of ME3M2H (Table I Figure 2). DISCUSSION These results suggest that the cross-adaptation relationship previously observed between 3M2H and its ethyl esters (10) may be a general one, as the methyl esters displayed a strikingly similar pattern of effectiveness in reducing the perception of 3M2H intensity. Thus, the initial reduction in perception following 15 seconds of exposure (35.0% following exposure to EE3M2H vs 36.5% following ME3M2H exposure), the shape of the adaptation curve, and the overall reduction in perceived odor intensity (mean re- duction of 35.1% following EE3M2H exposure 34.3% following ME3M2H) are con- sistent between the ethyl and methyl ester exposures. In addition, this similarity was seen even though the methyl ester mixture contained three minor components whose homologues were not present in the ethyl ester mixture previously employed (10). Also of note is that a significant reduction in the perception of 3M2H was achieved by the methyl ester mixture this level of reduction was not seen either with the EE3M2P or EE3M20, which are stronger smelling, fruity homologues of EE3M2H (10). Subsequent studies will include a purified mixture of only the E-Z-methyl ester isomers and/or the E- and Z-isomers alone, as per our previous studies (9). These results, suggesting a possible receptor interaction for an acid and its esters, have a neurophysiological parallel. Sato et al. (15) examined tuning specificities in mouse

374 JOURNAL OF COSMETIC SCIENCE Exposure to the Methyl Esters of 3M2H -a- M-3M2H ' +' 3M2H 125 100 75 5O 25 Exposure to 3M2H -'•- 3M2H ' +' M-3M2H !1• Recove!I•1'+II' , !, • II ' • ,,-.I .t. I ..+"• I ' +fi t4)]• I.' Adaptation "" •'"" "- • l•,, • •'•' 'l-If •11 • b , , , i . . , I . . . i , . . i . . • I • , , i , , , i , . . i . , . I . I i I 1 2 3 4 5 6 7 8 9 lO Time (min) Figure 2. Mean magnitude estimates (with standard errors) as a percentage of the initial estimates for 3M2H and ME3M2H following adaptation to each compound. olfactory receptor cells and found that sensitivity depended upon both carbon chain length and the terminal functional group (carboxyl, hydroxyl, or amino), with some cells responding specifically to an acid and its esters. Overall, these results further demonstrate that structurally similar, yet perceptually