Immuno-histochemical staining of Ki-67 on kidney sections of 0 days old SD and PKD2 mutant rats. (A) Images of a representative kidney section of 0 days old SD and PKD2 mutant rats stained with Ki-67 under 400× magnification. (B) Average number of Ki-67 stained nuclei per visual field in three SD (Nr. 34, 35 and 36) and three PKD2 mutant (Nr. 30, 31 and 32) rats. Data represent the mean ± SEM of Ki-67 positive cells in five different visual fields.