Figure 4. Immunolocalization of sirtuin 1 in the normal rat retina. Immunohistochemical staining showed that sirtuin 1 (SIRT1) was strongly expressed in the retinal ganglion cell (RGC) layer (GCL), inner nuclear layer (INL), outer nuclear layer, and photoreceptor layer (PRL; A). SIRT1 was also expressed in the optic nerve axon (B). The negative controls showed no detectable staining in retina (C, D).