Gustatory and olfactory-guided responsiveness to maltodextrin solutions in mice.

Rodents avidly consume maltodextrin solutions. Oligosaccharides appear to generate a detectable oral perception distinct from basic tastes in rodents and humans. Mice lacking one or both subunits of the T1R2 + T1R3 heterodimer still display relatively normal preference for maltodextrins but have severely blunted responsiveness to sugars. To test whether taste contributes to maltodextrin responsiveness, we performed lingual gustatory nerve transection (NX) in mice with [wild-type (WT)] and without [knockout (KO)] functional T1R3 subunits. Mice were then tested, after a ∼23-h fast, for concentration-dependent licking responses to Maltrin, a maltodextrin, and sucrose in a brief-access paradigm, which minimizes postingestive influences on responsiveness. Compared with SHAM mice, NX mice displayed blunted lick responses and initiated fewer trials to Maltrin. The KO mice exhibited some concentration-dependent licking to sucrose, though attenuated, which may be due to flavor-nutrient learning across sessions. However, NX blunted this responsiveness in all mice. The results suggest that an intact chorda tympani and/or glossopharyngeal nerve(s) is required for normal licking to maltodextrin and sucrose solutions, confirming a contribution of gustatory signals to behavior. A follow-up experiment tested whether olfactory signals contribute to Maltrin detection in mice trained in a Go/No-Go task. Mice could detect the volatiles associated with Maltrin in a concentration-dependent manner. As maltodextrins have negligible vapor pressure, mice are likely responding to volatile contaminants within the solution, which could potentially serve as cues for flavor-nutrient conditioning. Nevertheless, there is clearly a gustatory component that unconditionally drives hedonic responsiveness to this stimulus.