Multiple receptor sites mediate sweetness: evidence from cross adaptation.

The method of cross adaptation was implemented to determine whether only one type of receptor site mediates the perception of sweetness, or whether more than one such type exists. Fourteen stimuli, seven artificial sweeteners varying widely in chemical structure as well as seven sugars, were cross adapted with one another. When a sugar was employed as the adapting stimulus, a consistent reduction in the intensity of the test solution's sweetness was found. However, the result of the cross adaptation when the adapting stimulus was an artificial sweetener was unpredictable; it led not only to a reduction but, in some cases, to an enhancement or no change in the test solution's intensity, depending on its identity. In previous investigations, enhancements have been explained through the existence of a water taste. Since this explanation is insufficient to account for the enhancement effects found in this study, it appears that cross adaptation does not always occur between sweet-tasting compounds. For this reason, it is concluded that more than one receptor mechanism may be responsible for the perception of the sweet quality.