For determination of the LI with image analysis (see below), BrdU
primary antibody was detected using an fluorescein isothiocyanate
(FITC)-labeled secondary antibody (goat antimouse IgG; Boehringer
Mannheim). Control sections were incubated with normal goat serum
(Vector) or mouse ascites fluid in place of primary antibody. Sections
were counterstained with propidium iodide (PI; Molecular Probes, Eugene,
OR) to fluorescently label all cellular DNA (21).