Radial retinal sections were washed three times in PBS and incubated for 1 hour in a solution of PBS with 20% normal goat serum (NGS), 1% BSA, and 0.1% Triton X-100. Antibodies against the following Ca2+-binding proteins were used: calbindin-D-28K, clone CL-300 (mouse mAb, 1:200; Swant, Bellinzona, Switzerland), calretinin (rabbit pAb, 1:300; Chemicon, Temecula, CA), parvalbumin (rabbit pAb 1:5000; Swant), protein gene product 9.5 (PGP 9.5; rabbit pAb, 1:1000; Chemicon), protein kinase C (PKC), clone MC5 (mouse mAb, 1:100; Amersham, Buckinghamshire, England), recoverin (rabbit pAb, 1:500; gift from K.-W. Koch, Jülich, Germany), and TrkB (rabbit pAb, 1:100; Transduction Laboratories, Lexington, KY) at 4°C. Standard streptavidin-biotin method (DAKO Diagnostica, Glostrup, Denmark) was used, and fluorescent immunostaining was detected with Cy3-labeled goat anti-mouse antibody (1:500) (Rockland, Gilbertsville, PA). Apoptosis was determined by terminal transferase dUTP nick-end labeling (TUNEL; Roche Diagnostics GmbH, Mannheim, Germany).