PACAP treatment has also been shown to significantly attenuate the UVA-induced retinal damage, which was in accordance with our findings that PACAP and CHC inhibited UVB-induced apoptosis in RGC5 cells. Structural analysis has shown that the N-terminus of PACAP is flexible and disordered, while C*HSDGIC* synthesized from cyclizing HSDGI and adding two Cys residues at both ends is more stable with a more fixed conformation. Furthermore, CHC has a small molecular weight, which allows it to easily penetrate the blood-retina barrier. CHC is also a selective agonist of PAC1 without inducing side effects mediated through other receptors of PACAP. PAC1 has gained considerable attention because it has been shown to mediate the anti-apoptotic and cytoprotective effects of PACAP and accumulating studies have noticed the value of detecting PAC1 expression in retinal cells. To confirm the results of western blot analysis in our previous studies, immunocytochemistry was performed on RGC-5 cells with Thy-1 and PAC1 antibodies. The RGC-5 cell line used in this study was positive for Thy-1, a specific marker for RGCs. Immunofluorescence also showed diffuse expression of PAC1 antigen, the putative target for PACAP analogs. Currently there is controversy over the validity of RGC-5 cells. Recent publications emerged claiming that the RGC-5 cell line wasn’t derived from rat but from mouse and was actually a photoreceptor cell line 661W. The antibodies against Thy-1 and PAC1 used in our studies detect antigens of both mouse and rat origin, so we cannot exclude the possibility that the RGC-5 cell line is from mouse and not rat origin. However, we tend to be reticent about the opinion that RGC-5 cells are ganglion cell-like cells, because the RGC-5 cells used in our studies were positive for Thy-1 labeling, which is a RGC specific marker. In our experience, similar to RGCs, the RGC-5 cells used were sensitive to oxidative stress and neurtrophin withdrawal. 661W cells resemble neuronal cells, demonstrating cellular and biochemical LY2109761 characteristics exhibited by cone photoreceptor cells. The authors deduced that the 661W cell line was also present in the RGC-5 originating laboratory, which probably resulted in cross contamination. If this is the reason, then we cannot help but wonder how the authors ensure that their conclusion wasn’t also a mischaracterization due to cross contamination since the phenotypic origin of RGC-5 was detected with 661W? Also the hypothesis of RGC-5 cells being photoreceptors cannot explain the evident labeling for Thy-1 in the current studies. As the two cell types are very different by molecular phenotyping, it is difficult to reconcile this discrepancy. In fact, the same group who published this recent report previously used RGC-5 cells for other studies, confirming their retinal ganglion cell origin. Even though RGC-5 cells are not so ideal a model of RGCs as they were once considered, they still represent neuronal precursor cells which are useful for future neuroprotection type of investigations. The effects of PACAP on apoptosis have been studied in numerous in vitro and in vivo models. PACAP influences apoptotic signaling at various levels from initiation to down.