Mice Condition Cephalic Insulin Responses to the Flavor of Different Laboratory Chows

Background/Objectives: Cephalic-phase insulin responses (CPIRs) are characterized as the pre-absorptive release of insulin triggered by sensory stimuli associated with eating or drinking. CPIRs are beneficial because they reduce postprandial elevations in blood glucose. Methods: We investigated whether the flavor of two different types of laboratory chow elicits a CPIR in mice (C57BL/6). Results: First, we tried unsuccessfully to replicate a prior report that a single bite from a familiar chow pellet elicits a CPIR. Second, we determined that a minimum of 15 s of chewing on a familiar chow was necessary to elicit a CPIR. Third, we asked whether the chow-induced CPIR required prior exposure to the same chow. We tested the responses to a standard and a purified chow, which had similar macronutrient compositions. Mice raised on standard chow generated a CPIR to standard chow but not the novel purified chow. After 4 (but not 2) weeks of exposure to the purified chow, however, the mice generated a CPIR to it. Likewise, mice raised on purified chow generated a CPIR to purified chow but not to the novel standard chow. After 2-4 weeks of exposure to standard chow, however, the mice conditioned a CPIR to it. It follows that mice had to condition CPIRs to each type of chow. Fourth, we established that olfactory impairment eliminated the conditioned CPIR to standard chow (when it was familiar), but not to purified chow (when it was familiar). Conclusions: The flavor of familiar chow reliably triggered a CPIR in mice, but this response had to be conditioned through dietary exposure. Olfaction was a critical component of the conditioned stimulus for standard but not purified chow.