Olfactory sensitivity of mice to sugar solutions

Recent research indicates that odor cues may contribute to the detection or discrimination of sugar solutions, highlighting an important variable for gustatory researchers to consider. However, whether animals can directly detect volatile compounds emitted by sugar solutions has not yet been systematically tested. Further, studies in both rodents and humans have, thus far, utilized limited concentrations of these tastants, preventing gustatory researchers from fully assessing the potential impact of odor on their specific experiment. To address these shortcomings, we have performed a rigorous psychophysical examination of the orthonasal olfactory sensitivity of mice to the volatiles emanating from reagent-grade sugar solutions using a head-fixed Go / No-Go operant conditioning assay combined with highly reproducible stimulus delivery. C57BL/6J (WT) mice displayed high sensitivity to glucose (0.05M) and fructose (0.07M) but were slightly less sensitive to sucrose (0.14M). This phenomenon was not dependent upon canonical sweet taste signaling, as mice lacking the T1R3 subunit (T1R3KO) of the "sweet" taste receptor did not differ in their olfactory sensitivity to glucose as compared to WT mice. As these carbohydrates have negligible volatility, mice are likely responding to volatile contaminants associated with the tastants. These estimates of olfactory sensitivity to sugar solutions should be considered in the design and interpretation of taste-based paradigms in mice. Moreover, gustatory function, in general, should be evaluated in light of potential contributions from the olfactory system.