Perceptual and neural responses to sweet taste in humans and rodents

Abstract

Introduction: This mini-review discusses some of the parallels between rodent neurophysiological and human psychophysical data concerning temperature effects on sweet taste.

Methods and purpose: "Sweet" is an innately rewarding taste sensation that is associated in part with foods that contain calories in the form of sugars. Humans and other mammals can show unconditioned preference for select sweet stimuli. Such preference is poised to influence diet selection and, in turn, nutritional status, which underscores the importance of delineating the physiological mechanisms for sweet taste with respect to their influence on human health. Advances in our knowledge of the biology of sweet taste in humans have arisen in part through studies on mechanisms of gustatory processing in rodent models. Along this line, recent work has revealed there are operational parallels in neural systems for sweet taste between mice and humans, as indexed by similarities in the effects of temperature on central neurophysiological and psychophysical responses to sucrose in these species. Such association strengthens the postulate that rodents can serve as effective models of particular mechanisms of appetitive taste processing. Data supporting this link are discussed here, as are rodent and human data that shed light on relationships between mechanisms for sweet taste and ingestive disorders, such as alcohol abuse.

Results and conclusions: Rodent models have utility for understanding mechanisms of taste processing that may pertain to human flavor perception. Importantly, there are limitations to generalizing data from rodents, albeit parallels across species do exist.

Keywords: ethanol; neural coding; psychophysics; sweet; taste; temperature.

Figure 1

Effect of stimulus temperature on the perceived sweetness of sucrose in humans. Data represent magnitude estimates (ordinate) for a sucrose concentration series (abscissa) tested at 4°, 12°, 20°, 28°, 36°, and 44°C. Solid lines connect points representing responses to sequential concentrations measured at one temperature. Slopes for straight-line fits to data points acquired from 4° to 44°C are as follows: 1.31, 1.40, 1.02, 1.01, 0.89, and 0.80. Reprinted from Bartoshuk et al. (1982) with permission from the publisher.

Figure 2

The response of the chorda tympani nerve in rats to lingual delivery of 0.5 M sucrose tested at 10°, 20°, 30°, 40°, and 45°C. Points represent integrated, whole-nerve activity expressed relative to the response to a 0.1 M NaCl standard. Graph is reconstructed from data published in Yamashita and Sato (1965) with permission from the publisher.

Figure 3

Effect of stimulus temperature on neurophysiological activity to sucrose in taste-sensitive neurons in the mouse hindbrain. Data represent mean responses (spikes per unit time; ordinate) across 22 sucrose-oriented neurons to a sucrose concentration series (abscissa) tested at relatively cool (e.g., 18°C) to physiologically warm (37°C) temperatures. Data are plotted in doubly-logarithmic coordinates. Slopes for least-squares fits (solid lines) to activity to 0.1, 0.17, 0.31, and 0.56 M sucrose measured at 18°, 22°, 30°, and 37°C are as follows: 1.44, 0.94, 0.39, and 0.50. Dashed lines extend fits for comparison against activity to 0.05 M, a near-threshold concentration of sucrose (Treesukosol and Spector 2012). Reprinted from Wilson and Lemon (2014) with permission from the publisher.

Figure 4

Effect of temperature on the slope of the sucrose concentration-response function in mice and man. Lines represent least-squares fits of data points representing slopes (ordinate) for human psychophysical (Bartoshuk et al. 1982) and mouse neurophysiological (Wilson and Lemon 2014) concentration-response functions to sucrose tested at different temperatures (abscissa). Values for data point are given in Figures 1 and 3.