Post-oral glucose stimulation of intake and conditioned flavor preference in C57BL/6J mice: a concentration-response...

In a recent study, intragastric (IG) self-infusion of 16% glucose stimulated 1-h intake and conditioned a preference for a flavored saccharin solution in C57BL/6J mice (Zukerman et al., 2011). Experiment 1 of the present study presents a concentration-response analysis of IG glucose-induced intake stimulation monitored by recording licking response every min of the 1h/day sessions. Separate groups of food-restricted mice consumed a flavored saccharin solution (the CS-) paired with IG self-infusions of water (Test 0) followed by a different flavored solution (the CS+) paired with IG self-infusions of 2, 4, 8, 16, or 32% glucose (Tests 1-3). Following additional CS- and CS+ training sessions, a two-bottle CS+ vs. CS- choice test was conducted without infusions. Self-infusions of 8%, 16% or 32% glucose stimulated CS+ licking within 12 min of the first test session and even earlier in subsequent test sessions, and also conditioned significant CS+ preferences in the two-bottle test. The stimulation of early licking and CS+ preference increased as a function of glucose concentration. The amount of glucose solute self-infused increased with sugar concentration as did post-infusion blood glucose levels. The 2% glucose infusion did not stimulate CS+ intake and the 2% and 4% infusions failed to produce a CS+ preference in the 1-h test. Experiment 2 revealed that intraperitoneal self-infusions of 8% glucose, unlike IG glucose self-infusions, failed to stimulate CS+ licking or preference despite producing maximal increases in blood glucose levels. Taken together, these and other findings suggest that glucose rapidly produces concentration-dependent intestinal signals that stimulate intake and condition flavor preferences while post-oral satiation signals limit total amounts consumed.