Histological structure of the testis stained PCNA. (A, B): 3 months old rats before and after quercetin administration, respectively. In A, no reaction was observed was used as as we omitted PCNA antibody from the reaction and used it as a negative control. In B, Spermatogonia (black arrow), spermatocytes (white arrow), spermatids (black arrowhead) and Sertoli (white arrowhead) were positively immunostained with PCNA. (C, D): 30 months old rats before and after quercetin administration, respectively. In C, only spermatogonia (black arrow) were positively immunostained with PCNA. In D, spermatogonia (black arrow), spermatocytes (white arrow), spermatids (black arrow head) and Sertoli (white arrowhead) were positively immunostained with PCNA.