Figure 2.

Mean (±se) licking responses (after subtracting responses to water) during 5-s trials to various concentrations of Polycose, sucrose, and sodium saccharin in a brief access test by mice lacking either the T1R2 (top panels) or T1R3 (bottom panels) protein (KO:open circles) as well as by their wild-type controls (WT:closed circles) [from 48]. Knocking out the Tas1r2 or Tas1r3 genes eliminated concentration-dependent responses to sodium saccharin. The responses of the KO mice to sucrose were severely blunted relative to WT mice, but the KO mice did show some degree of responsiveness to high concentrations which was more evident in the subset of animals that were previously tested with Polycose. In contrast, KO mice displayed relatively normal concentration-dependent licking to Polycose. This latter finding suggests that either the T1R2 or T1R3 subunits alone are sufficient or that other receptors are involved in the maintenance of responses to some glucose polymers in the absence of either T1R2 or T1R3 [see also 47]. Reprinted with permission from the American Physiological Society.