Retinal pigmentation, visual acuity and brightness levels.

This study investigates the hypothesis that the degree of retinal pigmentation in the human eye is adaptive as it relates to the maintenance of visual acuity in optically stressful environments, deserts and snowfields. Eighty-four subjects were examined, an estimation of their degree of retinal pigmentation made by ophthalmoscopic examination and their binocular visual acuity tested over ten levels of brightness. The general level of retinal pigmentation did not influence mean visual acuity within the levels of brightness used in this study. The hypothesis was, therefore, rejected, but with the proviso that this study should be extended to even higher levels of brightness than were obtained here. There was no difference in mean pupil size at various levels of illumination between individuals grouped by degree of retinal pigmentation.     

Retinal prostheses: Clinical results and future challenges

Retinal prostheses aim at restoring visual perception in blind patients affected by retinal diseases leading to the loss of photoreceptors, such as age-related macular degeneration or retinitis pigmentosa. Recent clinical trials have demonstrated the feasibility of this approach for restoring useful vision. Despite a limited number of electrodes (60), and therefore of pixels, some patients were able to read words and to recognize high-contrast objects. Face recognition and independent locomotion in unknown urban environments imply technological breakthroughs to increase the number and density of electrodes. This review presents recent clinical results and discusses future solutions to answer the major technological challenges.     

Development of retinal layers

A noticeable characteristic of nervous systems is the arrangement of synapses into distinct layers. Such laminae are fundamental for the spatial organisation of synaptic connections transmitting different kinds of information. A major example of this is the inner plexiform layer (IPL) of the vertebrate retina, which is subdivided into at least ten sublayers. Another noticeable characteristic of these retina layers is that neurons are displayed in the horizontal plane in a non-random array termed as mosaic patterning. Recent studies of vertebrate and invertebrate systems have identified molecules that mediate these interactions. Here, we review the last mechanisms and molecules mediating retinal layering.     

Large-Scale Purification of Porcine or Bovine Photoreceptor Outer Segments for Phagocytosis Assays on Retinal Pigment Epithelial Cells

Analysis of one of the vital functions of retinal pigment epithelial (RPE) cells, the phagocytosis of spent aged distal fragments of photoreceptor outer segments (POS) can be performed in vitro. Photoreceptor outer segments with stacks of membranous discs containing the phototransduction machinery are continuously renewed in the retina. Spent POS are eliminated daily by RPE cells. Rodent, porcine/bovine and human RPE cells recognize POS from various species in a similar manner. To facilitate performing large series of experiments with little variability, a large stock of POS can be isolated from porcine eyes and stored frozen in aliquots. This protocol takes advantage of the characteristic of photopigments that display an orange color when kept in the dark. Under dim red light, retinae are collected in a buffer from opened eyecups cut in halves. The retinal cell suspension is homogenized, filtered and loaded onto a continuous sucrose gradient. After centrifugation, POS are located in a discrete band in the upper part of the gradient that has a characteristic orange color. POS are then collected, spun, resuspended sequentially in wash buffers, counted and aliquoted. POS obtained this way can be used for phagocytosis assays and analysis of protein activation, localization or interaction at various times after POS challenge. Alternatively, POS can be labeled with fluorophores, e.g., FITC, before aliquoting for subsequent fluorescence quantification of POS binding or engulfment. Other possible applications include the use of modified POS or POS challenge combined with stress conditions to study the effect of oxidative stress or aging on RPE cells.     

The expression analysis of Sfrs10 and Celf4 during mouse retinal development

Processing of mRNAs including, alternative splicing (AS), mRNA transport and translation regulation are crucial to eukaryotic gene expression. For example, >90% of the genes in the human genome are known to undergo alternative splicing thereby expanding the proteome production capacity of a limited number of genes. Similarly, mRNA export and translation regulation plays a vital role in regulating protein production. Thus, it is important to understand how these RNA binding proteins including alternative splicing factors (ASFs) and mRNA transport and translation factors regulate these processes. Here we report the expression of an ASF, serine-arginine rich splicing factor 10 (Sfrs10) and a mRNA translation regulation factor, CUGBP, elav like family member 4 (Celf4) in the developing mouse retina. Sfrs10 was expressed throughout postnatal (P) retinal development and was observed progressively in newly differentiating neurons. Immunofluorescence (IF) showed Sfrs10 in retinal ganglion cells (RGCs) at P0, followed by amacrine and bipolar cells, and at P8 it was enriched in red/green cone photoreceptor cells. By P22, Sfrs10 was observed in rod photoreceptors in a peri-nuclear pattern. Like Sfrs10, Celf4 expression was also observed in the developing retina, but with two distinct retinal isoforms. In situ hybridization (ISH) showed progressive expression of Celf4 in differentiating neurons, which was confirmed by IF that showed a dynamic shift in Celf4 localization. Early in development Celf4 expression was restricted to the nuclei of newly differentiating RGCs and later (E16 onwards) it was observed in the initial segments of RGC axons. Later, during postnatal development, Celf4 was observed in amacrine and bipolar cells, but here it was predominantly cytoplasmic and enriched in the two synaptic layers. Specifically, at P14, Celf4 was observed in the synaptic boutons of rod bipolar cells marked by Pkc-α. Thus, Celf4 might be regulating AS early in development besides its known role of regulating mRNA localization/translation. In all, our data suggests an important role for AS and mRNA localization/translation in retinal neuron differentiation.     

Interaction of Neuropeptides and Cultured Glial (Müller) Cells of the Chick Retina: Elevation of Intracellular Cyclic AMP by Vasoactive Intestinal Peptide and Glucagon

Vasoactive intestinal peptide (VIP) and, to a lesser extent, glucagon were found to increase intracellular cyclic AMP rapidly in cultured glial (Müller) cells of the chick embryo retina. Although VIP elicited higher cyclic AMP accumulation than glucagon at each concentration tested, the half-maximal concentrations were similar, i.e., 6 X 10(-8) M for VIP and 8 X 10(-8) M for glucagon. Secretin had a minimal effect on cyclic AMP accumulation even at a very high (5 X 10(-6) M) concentration. Several other peptide and nonpeptide putative agonists also had little effect on cyclic AMP accumulation. The cultured Müller cell may thus be a useful model for examining VIP and glucagon effects on glial elements of the CNS.     

青光眼视网膜神经节细胞凋亡机制研究进展

青光眼是由视网膜神经节细胞(Retinal ganglion cells,RGCs)死亡引起的一种疾病,最终能导致失明。近年来,关于高眼压(elevated intraocular pressure,IOP)引发的视网膜的特定分子途径等方面的信息逐渐增多。青光眼中视网膜神经节细胞的状态取决于视网膜神经节细胞促存活和促死亡途径之间的平衡,而有关这些反应的具体机制有较多的研究,但仍只能解释部分现象。本文综述了关于视网膜神经节细胞的凋亡、凋亡通路途径及可能引发损伤条件的最新研究进展。