An important step in bromodeoxyuridine (BrdU) immunohistochemistry is the production of single-stranded DNA to make the incorporated BrdU accessible to the antibodies. This paper examines the effect of distinct DNA denaturation pretreatments (DNase I, sodium citrate buffer, endonuclease Eco RI and exonuclease III, and HCl hydrolysis) on detection of BrdU. We found that all the methods used in the partial denaturation of DNA combined good nuclear immunostaining with acceptable tissue integrity. We also observed that these immunohistochemical protocols revealed a spatial pattern in the distribution of DNA-synthesizing cells within the cerebellar external granular layer (EGL) of 10-day-old rats, allowing us to estimate the fraction of S-phase cells. Our results indicate that detection of BrdU-stained cells is affected by the distinct histological procedures used in such detection. Additionally, as the duration and phases of the cell cycle in EGL neuroblasts are estimated in accordance with BrdU detection, an effect on this detection can render the measurement of cell cycle inaccurate. The present work shows that DNase I and citrate buffer, at appropriate conditions, may be good alternatives for acid denaturation. However, they are less sensitive than autoradiographic techniques that use 3H-thymidine administration. Finally, current data reveal that short survival times after a single BrdU exposure do not seem to affect the cell cycle progression of the EGL neuroblasts.
Keywords: BrdU immunohistochemistry; Cell cycle; Cerebellum; DNA denaturation; External granular layer.