Detection of maltodextrin and its discrimination from sucrose are independent of the T1R2 + T1R3 heterodimer

Abstract

Maltodextrins, such as Maltrin and Polycose, are glucose polymer mixtures of varying chain lengths that are palatable to rodents. Although glucose and other sugars activate the T1R2 + T1R3 "sweet" taste receptor, recent evidence from T1R2- or T1R3-knockout (KO) mice suggests that maltodextrins, despite their glucose polymer composition, activate a separate receptor mechanism to generate a taste percept qualitatively distinguishable from that of sweeteners. However, explicit discrimination of maltodextrins from prototypical sweeteners has not yet been psychophysically tested in any murine model. Therefore, mice lacking T1R2 + T1R3 and wild-type controls were tested in a two-response taste discrimination task to determine whether maltodextrins are ) detectable when both receptor subunits are absent and) perceptually distinct from that of sucrose irrespective of viscosity, intensity, and hedonics. Most KO mice displayed similar Polycose sensitivity as controls. However, some KO mice were only sensitive to the higher Polycose concentrations, implicating potential allelic variation in the putative polysaccharide receptor or downstream pathways unmasked by the absence of T1R2 + T1R3. Varied Maltrin and sucrose concentrations of approximately matched viscosities were then presented to render the oral somatosensory features, intensity, and hedonic value of the solutions irrelevant. Although both genotypes competently discriminated Maltrin from sucrose, performance was apparently driven by the different orosensory percepts of the two stimuli in control mice and the presence of a Maltrin but not sucrose orosensory cue in KO mice. These data support the proposed presence of an orosensory receptor mechanism that gives rise to a qualitatively distinguishable sensation from that of sucrose.

Electrophysiological responses to sugars and amino acids in the nucleus of the solitary tract of type 1 taste receptor double-knockout mice

“…This and similar stimuli, for example, Polycose, taste bland (though detectable) to humans (Lapis et al 2014) but produce strong preferences and hedonic responsiveness in rodents (Sclafani and Clyne 1987). Such motivated behavior as well as taste detection thresholds are relatively unaltered by T1R deletion (Smith and Spector 2017;Treesukosol et al 2009Treesukosol et al , 2011aTreesukosol and Spector 2012;Zukerman et al 2009). Consistent with the lack of a behavioral contribution of T1Rs, the incidence of Maltrin responses did not differ between double-KO and WT mice (9 vs. 13%, P Ͼ 0.1 2 -test) and the average response magnitude was only marginally greater in the WTs (WT: 8.1 Ϯ 1.8 and double-KO: 3.7 Ϯ 1.7, P ϭ 0.07).…”

“…Thus we used umami, MSG with amiloride (MSGa), and MSG alone at an intense concentration of 0.6 M. In addition, two amino acids differentially affected by T1R deletion were included. Glycine detection is impaired but not abolished (Smith and Spector 2017) whereas L-lysine is relatively unaffected by T1R deletion Spector 2014, 2017). Similarly, although preference and discrimination for sugars is markedly diminished in mice devoid of the T1R2 and/or T1R3 subunits, behavior toward maltodextrin solutions is relatively unaltered (Smith and Spector 2017;Treesukosol et al 2009;Zukerman et al 2009).…”

“…Glycine detection is impaired but not abolished (Smith and Spector 2017) whereas L-lysine is relatively unaffected by T1R deletion Spector 2014, 2017). Similarly, although preference and discrimination for sugars is markedly diminished in mice devoid of the T1R2 and/or T1R3 subunits, behavior toward maltodextrin solutions is relatively unaltered (Smith and Spector 2017;Treesukosol et al 2009;Zukerman et al 2009). Thus Maltrin 580 (a generous gift of Grain Processing Corporation, Muscatine, IA), a glucose oligomer mixture with an average chain length of ~6, was also tested [Maltrin 580 is similar to Polycose (Ross Laboratories), the stimulus used in the original explorations of this polysaccharide taste, but this product is no longer available].…”

“…Indeed, the T1Rs are not significantly involved in transducing other types of carbohydrates. In particular, KO2ϩ3 mice display relatively normal behaviors toward Maltrin or Polycose, highly preferred oligosaccharide mixtures hypothesized to generate a distinct, nonsweet "polysaccharide" taste (Nissenbaum and Sclafani 1987;Smith and Spector 2017;Treesukosol and Spector 2012;Yee et al 2011). Likewise, the cephalic phase response elicited by glucose is dependent on the ATP-sensitive K ϩ (K ATP ) channel not T1R3 (Glendinning et al 2015(Glendinning et al , 2017.…”

Neural Isolation of the Olfactory Bulbs Severely Impairs Taste-Guided Behavior to Normally Preferred, But Not Avoided, Stimuli

“…Maltodextrins such as Maltrin are discriminable from sucrose by rodents (Nissenbaum and Sclafani, 1987;Smith and Spector, 2017). Both sucrose and maltodextrin are stimuli for which rodents display strong preferences in two-bottle intake tests and avidly lick in a concentrationdependent manner in brief access tests.…”