Fig. 3

Diet-induced obesity increases sensitivity to mechanical stimulation and alters spontaneous locomotion. a Mechanical sensitivity of the hind paw was assessed by manual application of Von Frey filaments using the Chaplin up-down method. Mice fed the western diet showed a significant decrease in withdrawal threshold at the 24- and 40-week time points compared to age-matched chow-fed controls, indicative of increased mechanical sensitivity. Mice fed a high-fat diet showed a significant decrease in withdrawal threshold at the 24-week timepoint compared to control. b Sensitivity to cold was assessed by measuring the time spent in behavior evoked by evaporative cooling of acetone (flicking, stamping, or licking of ventral surface of the paw) during the first 40 s following application of acetone to the ventral surface of the hind paw. No significant differences were seen between the diet groups at any timepoint. c Spontaneous locomotor activity was recorded over three 2-h sessions and averaged. Mice fed the western diet showed a significant decrease in the total distance traveled at the 12- and 24-week timepoint compared to age-matched chow-fed controls, while mice fed the high-fat diet showed a decrease at the 24-week timepoint. The number of rearing events was significantly decreased in mice fed the high-fat and western diets compared to controls at the 40-week timepoint. n = 9–16 animals per timepoint, per diet. Data are plotted mean ± 95% CI; data points for each mouse are graphed within each group. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 by 2-way ANOVA