Figure 1. Sigma receptor 1 is required for (+)-PTZ-mediated neuroprotection. RGCs were isolated from neonatal WT and σR1 KO mouse pups and cultured for 72 h. A: DIC images were captured of living cells. Subsequently, cells were treated with xanthine–xanthine oxidase (X:XO; 10 µM:2 mU/ml) in the presence or absence of (+)-PTZ (3 µM) for 18 h and were subjected to TUNEL analysis. The calibration bar=10 μm. B: Representative photomicrographs of data from the TUNEL assay in cells receiving no treatment, (+)-PTZ only, X:XO only, or X:XO and (+)-PTZ. Nuclei, labeled with DAPI, fluoresce blue, and TUNEL-positive cells fluoresce green (arrows). The calibration bar=50 μm. C: Quantification of TUNEL-positive cells; data collected from 9 fields for each treatment; experiments were repeated three times. Data are expressed as mean±SEM of the ratio of apoptotic cells to the total number of cells. (The asterisks denote that data are significantly different from control; **, p<0.01, ***, p<0.001).