The Cross-Adaptation of Green and Citrus Odorants

Abstract

In 1998, a set of straight chain aldehydes ranging in carbon chain length from seven to ten carbons were identified for their ability to excite olfactory receptor I-7 (OR-I7; Zhao et al. 1998). Several studies have examined the differences in physiological response to these odorants in mammals as well as the different psychophysical properties of these odorants. Octanal (C8) is the primary agonist of OR-I7 while hexanal, C6, does not excite OR-I7. The primary psychophysical difference between these two odorants is their perceptual quality, C8 is characterized as citrus and C6 is described as green (Kittel et al. 2008). Because ligands with similar odor qualities have been shown to cross-adapt, while those with differing odor qualities do not, one would predict C6 would not cross-adapt with C8, decanal (C10), and undecanal (C11) but C8, C10, and C11 would cross-adapt with each other. This study uses squeeze bottle sensory tests to examine the cross-adaptation and self-adaptation of hexanal, octanal, C10, and C11. Individuals evaluated the intensity of each odorant before and after smelling an adapting stimulus. Self-adaptation was measured for all four odorants. The strongest observed cross-adaptation occurred between odorant pairs C10–C11 while C10–C8, and C10–C11 showed slightly less cross-adaptation. Most importantly, cross-adaptation occurred between C6 and the three other stimuli to a significantly lesser degree. As predicted, C6 did not cross-adapt with any of the three other odorants; however, the three citrus odorants did readily cross-adapt suggesting adaptation is a peripheral process.