MORPHOLOGICAL FEATURES OF THE RETINAL-PIGMENT EPITHELIUM IN THE TOAD,BUFO-MARINUS

Background: The toad's (Bufo marinus) retinal pigment epithelium (RPE) has been used in many studies as a model for understanding its role a nd interaction with the neural retina (NR), In this study, the fine st ructure of the RPE is described, Methods: In vitro RPE-chorion prepara tions from the toad were studied after separation from the NR. Tissues were processed for light and electron microscopy. Results: The RPE co nsists of a single layer of cells joined by a series of tight junction s forming part of the blood-retina barrier. These cells had minimal in folding of the basal membrane and numerous microvillous processes exte nding from the apical surface and surrounding photoreceptor outer segm ents, Internally, RPE cells display a large nucleus, numerous mitochon dria located at the basal membrane, extensive smooth endoplasmic retic ulum, myeloid bodies, phagosomes, scattered polysomes, large lipid dro plets and melanin granules, Rough endoplasmic reticulum is relatively scarce within these cells, The choriocapillaris consists of large bloo d vessels facing Bruch's membrane, Bruch's membrane is typical of othe r vertebrates, being pentalaminate over the whole retina. The endothel ium of the choriocapillaris facing Bruch's membrane is typically very thin but shows few fenestrations, Conclusions: Due to the ultrastructu ral similarities of toad RPE with that of mammals, it can serve as an excellent model for the study of retinal detachment/reattachment and t heir cellular and molecular mechanisms. (C) 1997 Wiley-Liss, Inc.