Abstract
Taste is the sensory system primarily responsible for selection of food to be ingested. In this sense, the ability to taste the sweetness is important for animals to detect carbohydrate source of calories and has a critical role in the nutritional status of animals. Our recent studies suggested that sweet-sensitive cells may act as sensors not only for external calorie sources but also for internal energy store, represented by plasma leptin level, and external temperature (15-35oC). Decrease in plasma leptin level and increase in temperature enhance sweet sensitivity of taste cells. Such modulation of perceived sweetness transmitted to the brain through afferent fibers may help maintaining animal's energy homeostasis. Recently, it is reported that taste cells expressing sweet or bitter receptors, such as T1rs and T2rs, have no conventional synapses with taste axons, providing a new taste mystery on peripheral information transmission. To challenge this mystery, we compared response characteristics of mouse fungiform taste receptor cells with action potentials and chorda tympani nerve fibers. We found that taste cells and fibers share similar characteristics in (1) response selectively to the four basic taste stimuli, (2) the grouping based on hierarchical cluster analysis, and (3) the occurrence of each class of taste cells with different taste responsiveness. These results suggest that information derived from receptor cells generating action potentials may be transmitted to taste nerve fibers with no major modifications by some unknown system. [J Physiol Sci. 2007;57 Suppl:S39]
