Comparative histology of 1-month-old c57 and P347S retinas. Eyes from 1-month-old c57 and P347S (mutant pro347ser RHO transgene) animals were fixed in 4% paraformaldehyde, 12 μm cryosections cut, and nuclei counterstained with 4',6-diamidine-2-phenylindole-dihydrochloride (DAPI). Phase contrast and fluorescent dark field (DAPI, false colored) microscopic images were overlaid to display histology of (a) P347S and (b) c57 retinas. Combined thicknesses of photoreceptor outer an inner segments (yellow arrows) and outer nuclear layer (magenta arrows) are indicated. Scale bar: 25 μm. GCL, ganglion cell layer; INL, inner nuclear layer; IS, photoreceptor inner segments; ONL, outer nuclear layer; OS, photoreceptor outer segments.