Figure 9.

Insulin IND treatment only slightly affects odorant threshold and does not affect time to decision or the number of choices in a two-choice paradigm for odorant threshold. A, Line graph of the mean body weight for awake IND-treated mice in which either insulin (●) or boiled insulin (○) was administered on days 7–12. Body weights were carefully lowered via food restriction to 75–85% ad libitum feeding body weight during important days of the two-choice paradigm in which mice were scored for correct decision (dig) to receive a hidden food reward (honey-flavored cereal) buried under peppermint-scented litter. Working trial days are denoted by underlining and start of the IND treatment is indicated by the arrow. B–D, Histogram plot of the percentage correct decision (B), the time to reach decision (C), and the number of transitions before decision versus odorant concentration (D) represents the mean (±SEM) for 8 mice in each of the two treatment groups (insulin, solid bar; boiled insulin, open bar). Each property on the abscissa was plotted against successive 10-fold diluted odorant concentration as indicated on the ordinate (1 × 10^−x). Acquisition of behavior task took place on testing days 4–6, during which mice first fell at or below 80% correct decision (B, dashed line). After 5 d of IND treatment (days 7–11), mice were retested at the 1 × 10⁻⁸ odorant concentration (day 12) through a series of dilutions until odorant detection threshold was reached (50% correct choice, equivalent to chance alone). Note: Insulin IND-treated mice were able to detect odorant at 1 log unit lower magnitude than that of boiled insulin-treated mice (B), but neither treatment yielded a significant difference in the time to make a decision (C) nor number of transitions between choices (D).