Immediately after euthanasia, eyes were enucleated and immersion fixed in 4% paraformaldehyde for 1 hour, washed in 0.1 M phosphate-buffered saline (PBS, pH 7.4), and cryoprotected by immersion in 15% sucrose overnight. Eyes were embedded in optimal cutting temperature (OCT) compound (Tissue Tek; Sakura Fintek, Torrance, CA), snap frozen in liquid nitrogen-isopentane and cryosectioned at 20 μm. Each eye was oriented so that sections ran from the superior to the inferior edge. Sections were collected on gelatin- and poly-l-lysine-coated slides. They were then immunolabeled for the following proteins: CNTF (Chemicon, Temecula, CA) 1:200, FGF-2 (Upstate Biotechnology, Lake Placid, NY) 1:200, CNTFRα (RDI, Flanders, NJ) 1:50, extracellular signal-regulated kinase (ERK) 1:50, phosphorylated ERK (pERK) 1:100 (Cell Signaling Technology, Beverly, MA), and FGFR1 1:100 (Santa Cruz Biotechnology Inc., Santa Cruz, CA). For all labeling, washes were performed three times for 5 minutes each in 0.1 M PBS at room temperature. To block nonspecific binding, 10% normal horse serum was used. Sections were incubated with antibodies at 37°C for 70 minutes. Antibodies against CNTF, FGFR1, ERK, and pERK were rabbit polyclonals, the antibody against CNTFRα was a goat anti-rat polyclonal, and the antibody against FGF-2 was mouse monoclonal.
Secondary antibodies were goat anti-mouse, goat anti-rabbit, or donkey anti-goat IgG conjugated to Alexa Fluor 488 (green) or 594 (red) diluted 1:200 in PBS (Molecular Probes, Eugene, OR) and incubated at 37°C for 1 to 2 hours, followed by three 5-minute washes in PBS, and counterstaining with DNA-specific label, bisbenzamide (Calbiochem, La Jolla, CA) 1:10,000 for 1 minute at room temperature (RT). Images were taken by laser scanning microscope (Leica, Deerfield, IL) and analyzed with NIH image (ImageJ 1.14c for Linux platform; available by ftp at zippy.nimh.nih.gov/ or at http://rsb.info.nih.gov/nih-image; developed by Wayne Rasband, National Institutes of Health, Bethesda, MD). Measurements of FGF-2 labeling were made across the full thickness of the ONL in the midperipheral retina (approximately half-way between the disc and the superior edge). Measurements of CNTF-labeling were made over an area covering the thickness of the INL, to include the most strongly CNTF-labeled elements in the retina, the somas of Müller cells.