Figure 1. Preexposure causes enhancement of odor avoidance. A, Typical examples of avoidance assay of the naive and the preexposed animals to 600 nl of 2-nonanone. Black dots indicate positions of the end points of animals' avoidance behavior. Positions of the odor source, the original position of animals and lines between the sectors were overlaid. B, Avoidance index of 2-nonanone avoidance after preexposure. The naive animals (“naive”) or animals kept in the absence (“mock”) or presence (“preexp.”) of 30 nl of 2-nonanone in NGM plates without food for 1 h were subjected to the avoidance assay with 600, 200 or 60 nl of 2-nonanone. The avoidance index reflects an average of avoidance distances of the animals from the center line of the plate. Open, gray, and solid bars indicate results of naive, mock-treated and preexposed animals, respectively, and each bar represents the mean ± SEM of 9 independent experiments throughout the figures unless otherwise indicated. C, 1-Octanol avoidance after preexposure. The animals were preexposed to 90 nl of 1-octanol without food for 1 h, and subjected to an avoidance assay with 60 nl of 1-octanol. D, The enhancement of 2-nonanone avoidance is AWB-dependent. Animals were preexposed to 90 nl of 2-nonanone in the absence of food for 1 h and then assayed with 600 nl of 2-nonanone. § indicates statistical difference from the corresponding wild-type index (see Results). E, Preexposure in the presence of food also caused the enhancement of 2-nonanone avoidance. The animals were preexposed to 30 nl of 2-nonanone in the presence of food and assayed with 600 nl of the odor. *p < 0.05, **p < 0.01 and ***p < 0.001 throughout figures.