Proliferation of parotid acinar and ductal cells following radiation (single 5 Gy dose) in FVB or IGF-1 injected mice. The head and neck region of FVB mice was exposed to a single 5 Gy radiation dose and mice received injections of IGF-1 or vehicle on days 4-8 as depicted in figure 1A. Parotid glands were removed 9, 30, 60, and 90 days after the radiation treatment. Tissues were embedded into paraffin and immunohistochemistry was performed using an antibody against PCNA. The graph represents the number of acinar cells with positive PCNA staining as a percentage of the total number of acinar (A) or ductal (B) cells in the field of view. The data is displayed as the mean and the standard error of the mean of all data from 3-8 mice per group. Significant differences (p < 0.05) were determined using an ANOVA followed by a post-hoc Bonferroni multiple-comparison test. Treatment groups with the same letters are not significantly different from each other within the same time point.