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At least 1,099 records · Page 61Linked to original sources
PubMed2003

Effect of acute hyperglycemia on oxygen and oxidative metabolism in the intact cat retina.

PURPOSE: The Crabtree effect is the phenomenon of inhibition of respiration by glycolysis, as a result of elevated glucose levels. It is not certain whether the Crabtree effect occurs in the retina, which has a high glycolytic capacity. In the current study, in vivo photoreceptor oxygen consumption was examined during the normo- and hyperglycemic states in the dark-adapted cat retina to determine whether the Crabtree effect occurs in the outer retina. METHODS: Spatial profiles of oxygen tension were obtained in the cat retina, in vivo, with the use of oxygen microelectrodes during control conditions and acute (5.19 +/- 0.83 hour) episodes of hyperglycemia (blood glucose, >350 mg/dL). The outer retinal portions of the profiles were fitted to a model of oxygen diffusion to quantify photoreceptor oxygen consumption. RESULTS: Photoreceptor oxygen consumption did not significantly change during hyperglycemia compared with control conditions. Choroidal PO(2) decreased during hyperglycemia by an average of 5.8 +/- 7.4 mm Hg. This led to an increase in the fraction of O(2) used by the photoreceptors that was derived from the inner retina. Choroidal PO(2) did not recover when blood glucose levels were returned to normal. Average inner retinal PO(2) was not affected by the episodes of hyperglycemia. CONCLUSIONS: The Crabtree effect does not occur to any significant degree in the outer retina, because hyperglycemia did not affect photoreceptor oxygen consumption. Choroidal PO(2) decreased during hyperglycemia, and the oxygen deficit was made up by the retinal circulation.

Acute Disease↗
PubMed2003

Loss of MCT1, MCT3, and MCT4 expression in the retinal pigment epithelium and neural retina of the 5A11/basigin-null mouse.

PURPOSE: The neural retina expresses multiple monocarboxylate transporters (MCTs) that are likely to play a key role in the metabolism of the outer retina. Recently, it was reported that targeting of MCT1 and -4 to the plasma membrane requires association with 5A11/basigin (CD147). In the present study, the hypothesis that reduced amplitudes in the electroretinograms in the 5A11/basigin null mouse (Bsg(-/-)) may be linked to altered expression of MCTs was studied. METHODS: The expression and subcellular distribution of MCTs in Bsg(-/-) mice was analyzed by immunofluorescence microscopy with isoform-specific antibodies. Protein expression was analyzed by Western blot analysis, and mRNA expression was examined with RT-PCR. RESULTS: Immunofluorescence labeling of tissue sections from the Bsg(-/-) mice revealed a dramatic reduction in labeling with MCT antibodies. There was a loss of MCT1 labeling in the apical membrane of the RPE and in the neural retina. MCT3, which is expressed in the basolateral membrane of the RPE wild-type mouse, was expressed at very low levels in both the apical and basolateral membranes of the Bsg(-/-) mouse. There was no change in expression or distribution of the glucose transporter (GLUT)-1 in the RPE and retina of the Bsg(-/-) mouse. Western blot analysis of detergent-soluble lysates prepared from wild-type and Bsg(-/-) eyes confirmed that the levels of MCT1, MCT3, and MCT4 protein were severely reduced in Bsg(-/-) mice. RT-PCR analyses of mRNA levels from wild-type and Bsg(-/-) mice demonstrated that the MCT1 transcript was expressed at normal levels in Bsg(-/-) mice. CONCLUSIONS: In Bsg(-/-) mice, there is a severe reduction in accumulation of the MCT1 and -3 proteins in the RPE and a concomitant reduction in MCT1 and -4 in the neural retina supporting a role for 5A11/basigin in the targeting of these transporters to the plasma membrane. Decreased expression of MCT1 and -4 on the surfaces of Müller and photoreceptor cells may compromise energy metabolism in the outer retina, leading to abnormal photoreceptor cell function and degeneration.

Animals↗
PubMed2003

Mechanism by which brain-derived neurotrophic factor increases dopamine release from the rabbit retina.

PURPOSE: To determine whether BDNF modulates the release of dopamine from amacrine cells in the rabbit retina. METHODS: Isolated retinas from rabbits killed with pentobarbital were incubated in Krebs bicarbonate medium containing pargyline, nomifensine, and bovine serum albumin. The medium was changed at 10-minute intervals, and the dopamine in the resultant samples measured by HPLC. Five samples were collected to establish the spontaneous resting release of dopamine, and then the retina was exposed to BDNF for a further two collection periods. Double-label immunohistochemistry was used to identify tyrosine hydroxylase containing neurons and to localize TrkB (BDNF) receptors. RESULTS: Exposure of the retina to BDNF (70-150 ng/mL) caused a concentration-dependent increase in the release of dopamine. The maximum effect was produced by 150 ng/mL BDNF, which almost doubled the release. The BDNF-evoked release was abolished in low-calcium/high-magnesium medium. It was also prevented by the tyrosine kinase inhibitors k252a and genistein, the phospholipase inhibitor U73122, and the sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitors thapsigargin and cyclopiazonic acid. Antagonists of gamma-aminobutyric acid (GABA) and glutamate did not affect the BDNF-evoked release of dopamine. ELISA assay confirmed the presence of BDNF in the retina, and immunohistochemistry revealed that some tyrosine hydroxylase-containing neurons possessed TrkB receptors. CONCLUSIONS: BDNF quickly (within minutes) increases the release of dopamine from amacrine cells in the rabbit retina by an action that is likely to involve TrkB receptors. The mechanism linking TrkB receptor activation to the release of dopamine involves activation of phospholipase-Cgamma, with the subsequent production of IP(3) and calcium release from the endoplasmic reticulum. The resultant capacitative entry of calcium seems to be the actual trigger for BDNF-induced release of dopamine.

Animals↗
PubMed2003

Cellular localization of the MPP4 protein in the mammalian retina.

PURPOSE: Membrane protein, palmitoylated (MPP)-4 is a novel retina-specific member of the p55-like subfamily of membrane-associated guanylate kinases (MAGUKs). MAGUKs are known to act as scaffolding molecules for multiprotein complexes at specialized regions of the plasma membrane. The goal of this study was to characterize the MPP4 protein and to determine its location in the mammalian retina. METHODS: RT-PCR and 5' and 3' rapid amplification of cDNA ends (RACE) techniques were used to isolate and sequence the full-length bovine MPP4 cDNA. Polyclonal antisera against the bovine MPP4 protein were generated in rabbits immunized with synthetic peptides. Affinity-purified anti-MPP4 antibodies were used to investigate the properties and distribution of MPP4 in retina and transfected 293-Ebna cells by Western blot analysis and immunofluorescence microscopy. RESULTS: The full-length bovine MPP4 cDNA encodes a putative bovine MPP4 protein of 640 amino acids with a predicted molecular mass of 72.9 kDa. Affinity-purified anti-MPP4 antibodies specifically detected the MPP4 protein in extracts from retina and 293-Ebna cells transfected with the MPP4 cDNA. Immunofluorescence analyses revealed that both the bovine and porcine MPP4 proteins are localized in the connecting cilia and synaptic terminals of cone and rod photoreceptors. In addition, postsynaptic structures in the outer plexiform layer and three distinct bands in the inner plexiform layer were MPP4-positive. In porcine but not bovine retina, a subclass of cone bipolar cells were labeled with anti-MPP4. CONCLUSIONS: The concurrent presence of MPP4 in connecting cilia and synaptic structures suggests that MPP4 plays a role at membrane-cytoskeleton interfaces in distinct structural and functional compartments of bovine and porcine retinas. This work provides the basis for further investigations into the function of MPP4 as a retinal scaffolding molecule and its possible role in retinal disease.

Animals↗
PubMed2004

Downregulation of ATP synthase subunit-6, cytochrome c oxidase-III, and NADH dehydrogenase-3 by bright cyclic light in the rat retina.

PURPOSE: Retinas of albino rats born and raised in bright cyclic light (300-800 lux) are less susceptible to light-induced apoptosis than retinas of animals born and raised in dim cyclic light (5 lux). In this study, the objective was to study the mechanisms of neuroprotection in the bright cyclic light-reared retina by identification of differentially expressed genes with differential display (DD)-PCR. METHODS: Albino rats were born and raised in 5- or 400-lux cyclic light (12 hours on/off). At 6 to 8 weeks of age, animals were either killed to harvest retinas or exposed to 1700 lux illumination for 12 or 24 hours. The neuroprotection of 400-lux cyclic light rearing was evaluated by DNA fragmentation and quantitative histology. The differentially expressed candidate genes were identified by DD-PCR. Northern blot analysis was used to quantitate differential expression of selected genes. Differential expression of protein was determined by Western blot and enzyme activity analysis. Cellular localization of transcripts was determined by in situ hybridization. RESULTS: DNA fragmentation and quantitative histology results indicated that 400-lux cyclic light rearing protected the retina from light-induced apoptosis compared with 5-lux cyclic light rearing. DD-PCR analysis showed that a 283-bp expressed sequence tag (EST) was downregulated in retinas of rats raised from birth in 400-lux cyclic light. A BLAST search identified the EST as the 3'-terminal sequence of mitochondria-encoded NADH dehydrogenase subunit 3 (ND-3). Northern blot analysis showed that the EST hybridized to two mRNA transcripts, the larger of which was confirmed to encompass the adenosine triphosphate (ATP) synthase subunit 6 (ATPase-6), cytochrome c oxidase subunit III (CO-III), ND-3, and tRNA-Gly. Northern blot analysis demonstrated that CO-III and ATPase-6 were downregulated 1.8- and 2.3-fold by 400-lux cyclic light compared with 5-lux cyclic light, respectively; however, there was no change in cytochrome c oxidase subunit I and II (CO-I and -II) or in 12S ribosomal RNA (12S rRNA), a mitochondrial housekeeping gene. Western blot analysis using anti-CO-III antibody showed more CO-III protein in retinal mitochondria from dim-light-raised rats. The enzyme activity of CO was two times higher in retinal homogenates from dim-light-raised rats than those from bright-light-raised rats. In situ hybridization using a (35)S-labeled CO-III probe showed that the CO-III transcript was present and downregulated in most of the retinal layers of bright-light-reared animals. CONCLUSIONS: Rearing in cyclic light at 400-lux downregulates the expression of ATPase-6, CO-III, and ND-3 compared with rearing in 5-lux cyclic light. The authors hypothesize that these changes are adaptive responses to light stress that provide neuroprotection to retinal cells by elevating the level of stress-related factors and reducing the level of oxidized cytochrome c, the form that activates the apoptotic cascade of cell death.

Adaptation, Ocular↗
PubMed2004

Subthreshold transpupillary thermotherapy reduces experimental choroidal neovascularization in the mouse without collateral damage to the neural retina.

PURPOSE: Transpupillary thermotherapy (TTT) is currently being evaluated for treatment of choroidal neovascularization (CNV) in age-related macular degeneration. To optimize TTT for CNV, the effect was analyzed of invisible (subthreshold) or visible (threshold) doses of TTT on the normal mouse retina and on experimental CNV. METHODS: TTT was delivered to the normal retina of 42 mice with a diode laser at increasing power settings (50, 60, 70, or 80 mW), to obtain thermal lesions ranging from invisible (subthreshold) to visible (threshold) burns. CNV was induced in 53 mice by krypton laser photocoagulation of the fundus, after which the CNV lesions were treated with TTT (50, 60, or 80 mW). Eyes were enucleated 7 days after TTT and prepared for histology, and the CNV complex was evaluated on hematoxylin-eosin stained serial sections by measuring the maximum height of the CNV lesions. Ultrastructural changes were examined by transmission electron microscopy. RESULTS: Increasing the TTT laser power yielded gradually more visible effects. At 50 mW, which induced subthreshold burns, no damage was seen in the neural retina, retinal pigment epithelium (RPE), or choroid at any time point. By contrast, eyes treated with higher power exhibited progressively more damage to the neural retina, including a complete disruption of the outer nuclear layer. When TTT was applied to the laser-induced CNV lesions, the height of lesions was significantly reduced (P < 0.001) in response to all three power settings at 7 days after treatment. The mean relative thickness of the CNV lesion was 3.29 +/- 0.89 in untreated mice, whereas in TTT-treated mice it was 1.69 +/- 0.35, 1.69 +/- 0.41 and 1.70 +/- 0.17 at power settings of 50, 60, and 80 mW, respectively. The overlying neural retina showed no apparent damage with the 50- or 60-mW settings, whereas outer nuclear layer disruption occurred with a power of 80 mW. Electron microscopy confirmed the presence of vascular occlusion at 1 day and a fibrotic scar at 7 days after TTT. CONCLUSIONS: Subthreshold TTT can effectively occlude newly formed vessels and cause regression of the experimental CNV complex without damaging the neural retina. The results demonstrate the importance of using subthreshold laser power in experimental and clinical evaluation of TTT.

Animals↗
PubMed2005

Prolactins are natural inhibitors of angiogenesis in the retina.

PURPOSE: Disruption of the normally antiangiogenic environment of the retina leads to aberrant angiogenesis, the major cause of vision loss throughout the world. Prolactin (PRL), the hormone originally associated with milk production, can be proteolytically processed to 16K-PRL, a 16 kDa N-terminal PRL fragment with potent antiangiogenic and vasoconstrictive actions. This study was conducted to determine whether 16K-PRL is found naturally in the retina and plays a role in angiogenesis and vasodilation. METHODS: Expression of PRL mRNA in rat retina was determined by RT-PCR and in situ hybridization. Western blot was used to examine the expression of PRL and derived fragments in retinal homogenates. The role of PRL and 16K-PRL in the retina was studied by intravitreal injection of either antibodies against PRL or small interfering RNAs (siRNA), to suppress expression of retinal PRL mRNA. RESULTS: Rat retina expressed PRL mRNA in the outer nuclear, outer plexiform, inner nuclear, and ganglion cell layers. Both full-length PRL and N-terminal 16K-PRL were detected in retinal homogenates by polyclonal and monoclonal antibodies. The intravitreal injection of antibodies able to neutralize the actions of 16K-PRL increased the number of retinal blood vessels and capillary area by threefold. Furthermore, siRNA-mediated inhibition of PRL mRNA increased retinal neovascularization threefold and resulted in a significant increase in vasodilation. CONCLUSIONS: These results demonstrate that PRL is synthesized and cleaved to antiangiogenic 16K-PRL by retinal tissue and that these molecules play a key role in preventing angiogenesis in the healthy retina.

Angiogenesis Inhibitors↗
PubMed2005

Pharmacokinetics of conjunctivally applied nerve growth factor in the retina and optic nerve of adult rats.

PURPOSE: Nerve growth factor (NGF) has been shown to inhibit retinal ganglion cell (RGC) degeneration when injected intraocularly in animal models of ocular hypertension, optic nerve transaction, and ischemia. The present study sought to establish the bioavailability of topical NGF to the retina and optic nerve in rats. METHODS: Autoradiography was performed to evaluate whether exogenous (125)I-labeled NGF reaches the retina and optic nerve when applied topically to the rat conjunctiva. To quantify NGF levels, a highly specific immunoenzymatic test (ELISA) was performed on the retina, optic nerve, lens, sclera and serum of rats at different time points after administration of NGF (1-500 microg/mL). The physiological activity of topically applied NGF was evaluated by determining retinal brain-derived neurotrophic factor (BDNF) protein and mRNA levels by ELISA and RT-PCR, respectively. RESULTS: After topical conjunctival administration of NGF, high levels were detected in ocular tissues, including the retina and optic nerve, showing a peak increase 6 hours after administration at a concentration of 200 mug/mL. NGF treatment was associated with an increase in BDNF protein and mRNA levels in rat retina. CONCLUSIONS: These data demonstrate the bioavailability of NGF to the retina and optic nerve in rats when administered topically. These findings justify investigating the clinical effects of topical NGF therapy for treatment of posterior segment diseases.

Administration, Topical↗
PubMed2006

Calpain-specific proteolysis in primate retina: Contribution of calpains in cell death.

PURPOSE: One of the leading causes of blindness is retinal damage caused by the high intraocular pressure (IOP) in glaucoma. Previous studies in rats have suggested that the proteolytic enzyme calpain (EC 3.4.22.17) is involved in retinal cell death during ischemia and in acute high IOP. Ubiquitous, calcium-activated calpain-1 and -2 from monkey retina are highly homologous to rat calpains, although expression patterns in variants of tissue-specific calpain-3 are different between monkey and rodent retinas. Thus, the purpose of the present study was to investigate the involvement of calpain-induced proteolysis in retinal cell death in primates. METHODS: Calpain involvement in a simulated pathologic condition was examined by incubating monkey retinas in hypoxic conditions (95% N2 and 5% CO2) in RPMI medium without glucose. Endogenous tissue calpains were also directly activated in monkey and human retinal soluble proteins by incubating with 2.5 mM calcium. The resultant proteolysis of monkey retinal proteins was assessed by 2D electrophoresis (2-DE). RESULTS: In hypoxic retina, leakage of lactate dehydrogenase (LDH) from retinas into the medium increased, indicating cell death. LDH leakage was partially inhibited by the calpain inhibitor SJA6017. Calpain autolysis was observed, and the calpain-preferred substrate alpha-spectrin was proteolyzed. In retinal soluble proteins incubated with calcium, a total of 15 spots from 2-DE of retinal soluble proteins were identified by mass spectrometry. Proteolysis of major proteins, vimentin, beta-tubulin, alpha-enolase, and Hsp70 were confirmed by immunoblot analysis. Activation of calpains and proteolysis of these substrates were inhibited by the calpain-specific inhibitor SJA6017. CONCLUSIONS: Taken together, these results suggested that calpain activation in primate retinas could play an important role in cell death during hypoxia caused by elevated IOP from glaucoma.

Adult↗
PubMed1998

SPARC is expressed by ganglion cells and astrocytes in bovine retina.

SPARC (secreted protein, acidic and rich in cysteine)/osteonectin is a matricellular, counteradhesive glycoprotein that disrupts cell-matrix interactions, interacts with growth factors and components of extracellular matrix, and modulates the cell cycle, but appears to subserve only minor structural roles. SPARC is expressed in a variety of tissues during embryogenesis and remodeling and is believed to regulate vascular morphogenesis and cellular differentiation. Although usually limited in normal adult tissues, SPARC is expressed at significant levels in the adult central nervous system. Using a monoclonal antibody against bovine bone osteonectin, we have determined the localization of SPARC in newborn (3-day-old) and adult (4-8-year-old) normal bovine retinas. SPARC was present in the soma of ganglion cells and strong reactivity was found in ganglion cell axons. Muller cells displayed no immunoreactivity, but SPARC was present in retinal astrocytes that were identified by the astrocyte marker glial fibrillary acidic protein (GFAP). Newborn calf retina showed a staining pattern similar to that of adult retina but exhibited significantly reduced levels of SPARC. Minimal levels of SPARC protein were also detected in some capillaries of the inner retina of both newborn and adult animals, whereas large vessels were negative. The presence of SPARC in the retina was confirmed by Western blotting of retinal extracts. These data indicate that SPARC originating from bot h neurons and glia of the inner retina may be an important modulator of retinal angiogenesis. The increased expression of SPARC in adult relative to newborn retinal tissue also indicates that SPARC has an ongoing role in the maintenance of retinal functions.

Animals↗
PubMedDate not supplied

Storage of human fetal retina in optisol prior to subretinal transplantation.

We have previously reported that Optisol, a commercially available medium (Chiron Vision, Irvine, CA), is a favorable fluid for the storage of neural retina. We now characterize the cell survival and histologic integrity of the tissue following storage and then transplantation. Neural retinas from human fetal eyes obtained within 1 h or pregnancy termination were stored in Optisol-GS medium (containing TC-199 and MEM medium, 2.5% chondroitin sulfate, 1% dextran, HEPES buffer, gentamicin sulfate, 0.1 mmol/L nonessential amino acids, sodium bicarbonate, 1 mmol/L sodium pyruvate, and additional antioxidants), at 4 degrees C for the following time periods: 0, 1, 2, and 7 days, and then tested for viability. Retinas stored for 2 and 7 days were mechanically dissociated and grafted into the eyes of light-damaged Fischer 344 rats (17 animals, 28 eyes). Nontransplanted eyes received injections of vehicle only (5 animals, 6 eyes). All animals were immunosuppressed daily with cyclosporine (10 mg/kg). All experiments were conducted in strict accordance with institutional, federal, and ARVO guidelines. Cell viability averaged 94.8%, 90.2%, 83.2%, and 76.8% at 0, 1, 2, and 7 days storage, respectively. Light microscopy demonstrated that the fetal retina was preserved without evident changes for up to 48 h. Up to 7 days there was a good to very good preservation of the cells in the outer neuroblastic layer. One month after transplantation subretinal grafts of retinal tissue stored for 2 and 7 days in Optisol showed good integration with host retina and initial photoreceptor differentiation. Optisol is a widely used medium for the preservation of human corneas prior to transplantation. Our results show that this medium is also highly suitable for preserving human fetal retinas prior to transplantation.

Animals↗
PubMed2001

Expression of ionotropic glutamate receptors in the retina of the rdta transgenic mouse.

BACKGROUND: The expression of retinal CaMKII is up-regulated in the retina of the rdta mouse in which rod photoreceptors are genetically ablated. As ionotropic glutamate receptors are known substrates of CAMKII, this study set out to determine if the protein levels of ionotropic glutamate receptors in the rdta mouse retina are also affected. RESULTS: The NMDA receptor subunits (NR1, NR2A/B) and the GluR1; AMPA receptor subunit (GluR1) were examined in immunolabeled western blots. The results demonstrate that the amounts of NR1 and NR2A/B receptor subunits are significantly increased in crude synaptic membrane fractions isolated from retinae of the rdta mice when compared to their normal, littermate controls. The GluR1 receptor subunit and its phosphorylation are simultaneously increased in retinae of the rdta mice. CONCLUSIONS: These data indicate that the NMDA receptors and AMPA (GluR1) receptors are altered in the retinae of rdta mice that lack rod photoreceptors. Because the rods are lost at an early stage in development, it is likely that these results are indicative of synaptic reorganization in the retina.

Actins↗
PubMed2001

Visual field constriction: accumulation of vigabatrin but not tiagabine in the retina.

BACKGROUND: The antiepileptic drug (AED) vigabatrin (VGB) causes concentric visual field constriction. Anecdotal reports involving tiagabine (TGB) have implied that this may be a class effect of all AEDs with gamma-aminobutyric acid (GABA)-related actions. We investigated the pharmacokinetic and pharmacodynamic profiles of VGB and TGB in rat brain and eye. METHODS: Adult male rats (n = 8) were administered 0.9% saline (control), VGB (500 or 1,000 mg/kg), or TGB (5, 10, or 20 mg/kg). At 1 (TGB) and 4 hours (VGB) postdosing, the animals were killed, a blood sample was obtained, their brains were dissected into five anatomic regions, and the retina and vitreous humor were isolated from each eye. Samples were analyzed for GABA concentrations and the activity of the enzyme GABA-transaminase (GABA-T). Plasma and tissue drug concentrations were also determined. RESULTS: VGB treatment produced a decrease in the activity of GABA-T and a rise in GABA concentrations in all tissues investigated. This effect was most pronounced in the retina. VGB concentrations were as much as fivefold higher in the retina than in the brain. TGB was without effect on GABA concentrations and activity of GABA-T. TGB concentrations were notably lower in the retina than in the brain. CONCLUSIONS: Accumulation of VGB in the retina, with or without an increase in GABA, may be responsible for the visual field constriction reported clinically. In contrast, TGB had no effect on GABA concentrations and did not accumulate in the retina. These results suggest that TGB is unlikely to cause visual field defects in humans.

Animals↗
PubMed2004

The hedgehog pathway is a modulator of retina regeneration.

The embryonic chick has the ability to regenerate its retina after it has been completely removed. Here, we provide a detailed characterization of retina regeneration in the embryonic chick at the cellular level. Retina regeneration can occur in two distinct manners. The first is via transdifferentiation, which is induced by members of the Fibroblast growth factor (Fgf) family. The second type of retinal regeneration occurs from the anterior margin of the eye, near the ciliary body (CB) and ciliary marginal zone (CMZ). We show that regeneration from the CB/CMZ is the result of proliferating stem/progenitor cells. This type of regeneration is also stimulated by Fgf2, but we show that it can be activated by Sonic hedgehog (Shh) overexpression when no ectopic Fgf2 is present. Shh-stimulated activation of CB/CMZ regeneration is inhibited by the Fgf receptor (Fgfr) antagonist, PD173074. This indicates that Shh-induced regeneration acts through the Fgf signaling pathway. In addition, we show that the hedgehog (Hh) pathway plays a role in maintenance of the retina pigmented epithelium (RPE), as ectopic Shh expression inhibits transdifferentiation and Hh inhibition increases the transdifferentiation domain. Ectopic Shh expression in the regenerating retina also results in a decrease in the number of ganglion cells present and an increase in apoptosis mostly in the presumptive ganglion cell layer (GCL). However, Hh inhibition increases the number of ganglion cells but does not have an effect on cell death. Taken together, our results suggest that the hedgehog pathway is an important modulator of retina regeneration.

Animals↗
PubMed2005

Retinoic acid regulates the expression of dorsoventral topographic guidance molecules in the chick retina.

Asymmetric expression of several genes in the early eye anlagen is required for the dorsoventral (DV) and anteroposterior (AP) patterning of the retina. Some of these early patterning genes play a role in determining the graded expression of molecules that are needed to form the retinotectal map. The polarized expression of retinoic acid synthesizing and degrading enzymes along the DV axis in the retina leads to several zones of varied retinoic acid (RA) activity. This is suggestive of RA playing a role in DV patterning of the retina. A dominant-negative form of the retinoic acid receptor alpha (DNhRARalpha) was expressed in the chick retina to block RA activity. RA signaling was found to play a role in regulating the expression of EphB2, EphB3 and ephrin B2, three molecules whose graded expression in the retina along the DV axis is important for establishing the correct retinotectal map. Blocking RA signaling by misexpression of a RA degrading enzyme, Cyp26A1 recapitulated some but not all the effects of DNhRARalpha. It also was found that Vax, a ventrally expressed transcription factor that regulates the expression of the EphB and ephrin B molecules, functions upstream of, or in parallel to, RA. Expression of DNhRARalpha led to increased levels of RA-synthesizing enzymes and loss of RA-degrading enzymes. Activation of such compensatory mechanisms when RA activity is blocked suggests that RA homeostasis is very strictly regulated in the retina.

Animals↗
PubMed1990

A positional marker for the dorsal embryonic retina is homologous to the high-affinity laminin receptor.

In a search for determinants of positional information in the embryonic eye, we isolated two monoclonal antibodies that label strongly the dorsal part of the undifferentiated embryonic retina in mammals, bird and cold-blooded vertebrates. In the chick, the optic tectum is labeled in a corresponding fashion, the ventral tectum more heavily than the dorsal tectum. Through biochemical and molecular analysis both antibodies were found to recognize a protein that has been cloned repeatedly, first in a screen with antibodies to the '68K-laminin receptor' (Wewer et al. (1986) Cancer Res. 47, 5691-5698), a name that may not exhaustively describe its function. Western blots show the protein to be present in most or all tissues, and Western and Southern blots reveal a high degree of conservation in the detected signals up to invertebrates and bacteria. Despite the very strong and selective labeling of the dorsal retina in conventional immunohistochemical preparations, the protein and its mRNA are present in even amounts throughout the embryonic retina, as demonstrated by Western and Northern blots of bisected retinas, and immunohistochemically in retinas fixed with ethylene glycole bissuccinimide (EGS), an NH2-group crosslinker with very long spacer arm. This indicates that the dorsoventral asymmetry in the embryonic retina is not in the amount but in the configuration of this protein; whether this difference relates to laminin binding is not known.

Animals↗
PubMed1998

FGF1 patterns the optic vesicle by directing the placement of the neural retina domain.

Patterning of the bipotential retinal primordia (the optic vesicles) into neural retina and retinal pigmented epithelium depends on its interaction with overlaying surface ectoderm. The surface ectoderm expresses FGFs and the optic vesicles express FGF receptors. Previous FGF-expression data and in vitro analyses support the hypothesis that FGF signaling plays a significant role in patterning the optic vesicle. To test this hypothesis in vivo we removed surface ectoderm, a rich source of FGFs. This ablation generated retinas in which neural and pigmented cell phenotypes were co-mingled. Two in vivo protocols were used to replace FGF secretion by surface ectoderm: (1) implantation of FGF-secreting fibroblasts, and (2) injection of replication-incompetent FGF retroviral expression vectors. The retinas in such embryos exhibited segregated neural and pigmented epithelial domains. The neural retina domains were always close to a source of FGF secretion. These results indicate that, in the absense of surface ectoderm, cells of the optic vesicles display both neural and pigmented retinal phenotypes, and that positional cues provided by FGF organize the bipotential optic vesicle into specific neural retina and pigmented epithelium domains. We conclude that FGF can mimic one of the earliest functions of surface ectoderm during eye development, namely the demarcation of neural retina from pigmented epithelium.

Animals↗
PubMed2007

Morphometric analysis of the retina from horses infected with the Borna disease virus.

Borna disease (BD) is a fatal disorder of horses, often characterized by blindness. Although degeneration of retinal neurons has been demonstrated in a rat model, there are controversial data concerning whether a similar degeneration occurs in the retina of infected horses. To investigate whether BD may cause degeneration of photoreceptors and possibly of other neuronal cells at least at later stages of the disease, we performed a detailed quantitative morphologic study of retinal tissue from Borna-diseased horses. BD was diagnosed by detection of pathognomonic Joest-Degen inclusion bodies in the postmortem brains. Paraffin sections of paraformaldehyde-fixed retinae were used for histologic and immunohistochemical stainings. Numbers of neurons and Müller glial cells were counted, and neuron-to-Müller cell ratios were calculated. Among tissues from 9 horses with BD, we found retinae with strongly altered histologic appearance as well as retinae with only minor changes. The neuron-to-Müller cell ratio for the whole retina was significantly smaller in diseased animals (8.5 +/- 0.4; P < .01) as compared with controls (17.6 +/- 0.8). It can be concluded that BD in horses causes alterations of the retinal histology of a variable degree. The study provides new data about the pathogenesis of BD concerning the retina and demonstrates that a loss of photoreceptors may explain the observed blindness in infected horses.

Animals↗