title: Fine structure of the retinal pigment epithelium of Oreochromis niloticus L. (Cichlidae; Teleostei) in light- and-dark adaptation.
abstract: The fine structure of the retinal pigment epithelium (RPE) of the cichlid Oreochromis niloticus was investigated in both light- and dark-adaptation. The eyes of four light-adapted and from four dark-adapted O. niloticus were fixed routinely for light and transmission electron microscopy. The RPE consisted of a single layer of columnar cells showing minimal basal infolding but plentiful apical processes that in light-adaptation interdigitated with the photoreceptor outer segments. The epithelial cells were joined by a series of basally-located tight junctions. These cells showed a large vesicular nucleus, plentiful smooth endoplasmic reticulum and polysomes, but only small amounts of rough endoplasmic reticulum. Phagosomes, lysosome-like bodies, lipid droplets, and myeloid bodies were observed. The choriocapillaris was a single layer of large-caliber capillaries, and Bruch's membrane (complexus basalis) was a trilaminate structure typical of teleosts. The RPE melanosomes moved basally (sclerally) in dark-adaptation and apically (vitreally) during light-adaptation. Other morphological features which changed at least to some degree during retinomotor responses were: the location of the RPE nucleus; the location and electron density of the mitochondria; and the location, number, and size of the myeloid bodies. A number of unique morphological changes take place within the RPE cells of this species during the circadian cycle in addition to the movement of melanosomes characterized in other vertebrates.
authors.affiliation: Department of Zoology, The University of Western Australia, Nedlands, Australia.
authors.forename: C R
authors.initials: CR
authors.lastname: Braekevelt
authors.forename: S A
authors.initials: SA
authors.lastname: Smith
authors.forename: B J
authors.initials: BJ
authors.lastname: Smith
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D000818:Animals; D003623:Dark Adaptation / Q000502:physiology*; D007425:Intracellular Membranes / Q000648:ultrastructure; D008854:Microscopy, Electron; D008928:Mitochondria / Q000648:ultrastructure; D020419:Photoreceptor Cells, Vertebrate / Q000166:cytology / Q000502:physiology / Q000648:ultrastructure; D010857:Pigment Epithelium of Eye / Q000166:cytology* / Q000502:physiology* / Q000648:ultrastructure; D017210:Tilapia / Q000502:physiology*