Capsaicin-treated rats permanently overingest low-but not high-concentration sucrose solutions

The effect of capsaicin-induced chemical ablation of visceral afferents on 1-h liquid sucrose consumption was investigated in food-deprived rats. We f irst show that although 10% sucrose is permanently overconsumed by capsaici n-treated (CAPs) compared with vehicle-treated (VEHs) control rats, 40% suc rose is only overconsumed during the first but not subsequent 1-h exposures . Furthermore, one group of CAPs lost the overconsumption response at 20% w hen exposed to progressively increasing sucrose concentrations of 10-40%, a nd another group recovered the overconsumption response at 10% when exposed to a series of decreasing concentrations. Control rats ingested relatively constant volumes of sucrose over the range of 10, 15, and 20%, resulting i n significantly different energy intakes. In contrast, CAPs generally showe d a concentration-dependent decrease in volume intake, resulting in relativ ely constant energy intake. These results suggest that capsaicin-sensitive visceral afferents, likely from gastric distension and other preabsorptive sensors, provide major control over volume ingested. In the absence of thes e signals, rats initially overconsume, but rapidly learn to use other signa ls from capsaicin-resistant preabsorptive or postabsorptive sites, to contr ol future intake. This redundant satiety system appears to be sensitive to the osmotic value or caloric content of the unfamiliar food, but only if th is is above a threshold of about 15% sucrose.