Odor-Cued Bitter Taste Avoidance

In the course of our ongoing studies of odor-cued taste avoidance (OCTA) to measure olfactory capabilities in animals, we observed that mice could rapidly learn to use the vapor of the classical bitterant quinine hydrochloride to avoid contact with the tastant. Here we expand on this observation to determine which among several compounds generally classed as bitter could be detected at a distance. Since mice were initially naïve we were able to assess whether the vapors of the bitter compounds tested were innately aversive as are their tastes. CD-1 mice could readily use vapor cues from quinine hydrochloride, denatonium benzoate (DB), and 6-propyl-2-thiouracil to avoid their taste. Although mice did not hesitate to make contact with these solutions on their first exposure, they did learn to do so typically after only 1 or 2 exposures. Bilaterally bulbectomized mice did not learn or retain the ability to avoid quinine and DB solutions by vapor alone, implicating olfaction as the mode of detection. Saturated aqueous solutions of sucrose octaacetate and caffeine which are bitter to humans and some strains of mice were not aversive in our studies. The very low vapor concentrations of the 3 bitterant solutions that mice detected at a distance, suggest that impurities in the reagent grade solutions, rather than the bitter molecules themselves were the basis of detection. Implications of these findings for taste testing and the role of odor in food acceptance/rejections decisions are discussed.