Fig. 1.

Schematic depiction of the hypothesized gustatory pathways that contribute to perceptual/behavioral and physiological responses to sugars in rodents. Taste function can be divided into three primary domains—sensory-discriminative, ingestive motivation (appetitive and consummatory), and physiological reflexes. Separate, or at least partially separate, central circuitries are proposed to mediate each of these functional domains. Accumulating evidence suggests that at least two different classes of taste receptors for sugars exist in the periphery (see text). Our model posits that these receptors are differentially channeled into circuits subserving different taste functions. Accordingly, one class—the canonical T1R2 + T1R3 heterodimeric receptor—binds with many of the common sugars [glucose (red), fructose (grey), sucrose (red + grey)] and other sweeteners (not shown) and predominately feeds into sensory-discriminative and ingestive motivation pathways. The other class, which has yet to be identified, binds with glucose and sucrose (possibly as a result of glucose product from enzymatic breakdown via sucrase in the apical membranes of some taste receptor cells), but not fructose, and predominately feeds into pathways involved in the generation of physiological preparatory reflexes, such as the cephalic phase insulin response. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)