Assessment of cellular proliferation by BrDU immunohistochemistry. Immunohistochemistry was performed using mouse monoclonal anti-BrDU antibody to detect the presence of nuclear BrDU 24 hours after fetal intraperitoneal injection of BrDU (50 mg/kg) at 16 days of gestation. More than 50% of cells were immunopositive. Scale bar is 200 μm.