Effects of D-cis-diltiazem and Olaparib on calpain activity in rd1*Cngb1−/− retina. The calpain activity assay (blue) and an immunostaining for activated calpain-2 (yellow) were performed on wt (a,b) and rd1*Cngb1−/− retina. DAPI (grey) was used as nuclear counterstaining. Untreated rd1*Cngb1−/− retina (untr.; c,d) was compared to retina treated with D-cis-diltiazem (e,f) or Olaparib (g,h). The scatter plots show the percentages of ONL-positive cells for calpain activity (i) and activated calpain-2 (j) in the wt and treated rd1*Cngb1−/− retina compared with the rd1*Cngb1−/− control (untr.). Statistical significance was assessed using one-way ANOVA and Tukey’s multiple comparison post hoc testing performed between the control (rd1*Cngb1−/− untreated), 100-μM D-cis-diltiazem (D100), and 1-μM Olaparib (OLA1). In rd1*Cngb1−/−, only D-cis-diltiazem reduced the cells positive for activated calpain-2. In the calpain activity assay, untr. wt: 5 explants from 3 different mice; untr. rd1*Cngb1−/−: 11/11; D100 rd1*Cngb1−/−: 6/6; OLA1 rd1*Cngb1−/−: 6/6; in calpain-2 immunostaining, untr. wt: 6/3; untr. rd1*Cngb1−/−: 17/17; D100 rd1*Cngb1−/−: 10/10; OLA1 rd1*Cngb1−/−: 10/10; error bars represent SD; ns = p > 0.05 and ** = p ≤ 0.01. ToPro (red) and ONL = outer nuclear layer, INL = inner nuclear layer, GCL = ganglion cell layer. Scale bar = 50 µm.