Effect of food restriction on acquisition and expression of a conditioned odor discrimination in mice

Level of food restriction was manipulated in mice to assess its importance for the acquisition and expression of a conditioned odor discrimination. In training, animals were exposed to odors (either rose or lemon) presented on a piece of filter paper in a pot covered in bedding. For half of the conditioning trials, group paired received one odor (CS+) with sucrose, the unconditioned stimulus (us), under the bedding. For the remaining trials, they received the other odor (CS-) alone. Group CS-alone was also exposed to both odors, but neither odor was paired with sugar on any of the conditioning trials. During training, Group Paired mice that were food-restricted tended to dig more readily and longer in the odors, especially in the CS+ odor, than animals that were not restricted. Both restricted and nonrestricted PAIRED GROUPS dug more in the CS+ than in the CS- by the end of training, but the CS-alone mice dug very little in either. Following training, mice were exposed to both odors simultaneously in a discrimination test. Half the mice in each training food restriction condition were tested under food restriction, and half were not. Only PAIRED animals that were food-restricted in the test expressed an odor discrimination, digging only in the CS+. This occurred regardless of their previous restriction state in training. These data suggest that both food-restricted and nonrestricted mice can acquire an odor discrimination; however, expression of this odor discrimination depends on food restriction.