Several recent studies have shown that postoral sugar sensing rapidly stimulates ingestion. Here we explored the specificity with which early phase postoral sugar sensing influenced ingestive motivation. In Experiment 1, rats were trained to associate the consumption of 0.3M sucrose with injections of LiCl (3.0 mEq/kg IP, conditioned taste aversion) or given equivalent exposures to the stimuli, but in an unpaired fashion (UNPAIRED). Then, all rats were given two brief access tests to assess appetitive and consummatory responses to the taste properties of sucrose (0.01-1.0 M), 0.12M NaCl, and dH2O (in 10-s trials in randomized blocks). Intraduodenal (ID) infusions of either 0.3M sucrose or equiosmolar 0.15M NaCl (3.0 ml) were administered, beginning just before each test. For UNPAIRED rats, ID sucrose specifically enhanced licking for 0.03-1.0 M sucrose, with no effect on trial initiation, relative to ID NaCl. Rats with an aversion to sucrose suppressed licking responses to sucrose in a concentration-dependent manner, as expected, but the ID sucrose preload did not appear to further influence licking responses; instead, ID sucrose attenuated trial taking. Using a serial taste reactivity (TR) paradigm, however, Experiment 2 demonstrated that ID sucrose preloads suppressed ingestive oromotor responses to intraorally-delivered sucrose in rats with a sucrose aversion. Finally, Experiment 3 showed that ID sucrose preloads enhanced preferential licking to some representative tastants tested (sucrose, Polycose, and Intralipid), but not others (NaCl, quinine). Together, the results suggest the early phase reinforcing efficacy of postoral sugar is dependent on the sensory and motivational properties of the ingesta.
- gustatory system
- nutrient sensing
- Copyright © 2016, American Journal of Physiology-Regulatory, Integrative and Comparative Physiology