Immunohistochemistry for caspase-3 was performed according to previously described methods [15 (link),16 (link)]. The sections were incubated overnight with caspase-3 antibody (1:500; Santa Cruz Biotechnology, Santa Cruz, CA, USA). The next day, the sections were incubated with biotinylated mouse secondary antibody (1:200; Vector Laboratories) for 1 hour. The secondary antibody was amplified with a Vector Elite ABC kit (1:100; Vector Laboratories). Antibody-biotin-avidin-peroxidase complexes were visualized using 0.03% DAB. The sections were mounted onto gelatin-coated slides, and the coverslips were mounted using Permount (Fisher Scientific).