Morphological study of retina in RCS rats during retinal degeneration

Objective To investigate morphological changes of retina in the Royal College of Surgeons (RCS) rats with the onset and development of retinitis pigmentosa (RP). Methods The RCS rats with inherited retinal dystrophy were divided into 3 groups: an initial stage group (RCS 15 d), a mid-stage group (RCS 30 d) and an advanced stage group (RCS 90 d) according to the severity of degeneration (n=5 animals in each group). These were compared with RCS-rdy+p+ rats without retinal degeneration (control groups, C 15 d, C 30 d, C 90 d). One retina of every animal was prepared for retinal slices and stained using hematoxylin-eosin (HE) method (The contralateral retina was prepared for other experiments). The thickness of outer segments (OS), outer nuclear layer (ONL) and inner nuclear layer (INL) was measured by MIAS-1000 image analysis system under light microscope. Results Photoreceptors of RCS rats were degenerated progressively. At late stage of retinal degeneration the structures of the retinal pigment epithelium (RPE) and photoreceptors layer were disorganized, but the morphology of inner nuclear layer and retinal ganglion cell (RGC) layer appeared normal. Compared with control groups, the breakdown of RPE caused a piling up of OS membranous disc photoreceptors of RCS rats with the onset and development of RP, and ONL thinning. However, INL was thickening in RCS 30 d, 15 d, and 90 d groups as compared with control groups. Conclusion The morphology of each layer neurons of retina in RCS rats remains change discordantly with the onset and development of RP. The thicker INL of retina in RCS rats in mid-stage group is possibly related with the reactive hyperplasia of cell processes and retinal morphology remodeling, which is resulted from lacking of signal input of fore-level neurons in retina INL.