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At least 613 records · Page 34Linked to original sources
PubMed1984

Cyclic nucleotide content and phosphodiesterase activity in the rds mouse (020/A) retina.

Cyclic nucleotide metabolism was examined in the retina and in the retinal pigment epithelium (RPE)-choroid complex of the rds mouse (020/A), a mutant in which discrete photoreceptor outer segment disc structures fail to develop. In retinas of both rds and control (Balb/c) mice, cyclic AMP levels peak at 10-15 days (20-25 pmol mg-1 protein). The level drops to about 10 pmol mg-1 at about one month in normal retinas but remains high in affected retinas. Cyclic GMP levels increase five-fold in Balb/c retinas as ROS develop whereas, in affected retinas, the levels remain constant and low (about 5 pmol mg-1). In RPE-choroid, cyclic nucleotide levels are similar in control and affected mice. Cyclic AMP phosphodiesterase (PDE) activity is somewhat higher in affected than in control retinas; conversely, cyclic GMP-PDE is lower. Both cyclic AMP-PDE and cyclic GMP-PDE activities are different in normal and affected RPE-choroid. Thus, although the rds (020/A) mouse belongs to the early-onset photoreceptor dysplasia group of hereditary retinal degenerations on a morphological basis, it does not exhibit high retinal cyclic GMP levels and thus appears to be distinct from other animals exhibiting early postnatal photoreceptor dysfunction.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1986

The horizontal cells in the retina of the owl, Tyto alba, and owlet, Carinae noctua.

One type of short-axon horizontal cell (HC) and one type of axonless HC are described in the retina of Carinae noctua, a crepuscular bird and Tyto alba, a pure nocturnal bird. The axonless HCs in both birds are similar to type II axonless HC found in diurnal birds. The short-axon HC of Carinae noctua is similar to the same cell type found in diurnal birds; the only difference being the axon length. The short-axon HC of the Tyto alba retina is morphologically different from the same cell type found in the retina of diurnal birds and Carinae noctua and very similar to the short-axon HC described in the mammalian retina and the primate retina in particular. The striking similarity between the short-axon HCs found in the retina of owl and primates may be related to the same rod-cone ratio found in these retinas.

Animals↗
PubMed1989

Diffusion of O2 in the retina of anesthetized miniature pigs in normoxia and hyperoxia.

Intraretinal oxygen tension (pO2) and local electroretinogram (ERG) were simultaneously measured in miniature pigs using double-barreled recess type microelectrodes. Transretinal pO2 profiles were recorded during normoxia and hyperoxia in areas close to (juxta-arteriolar) or far from (intervascular) retinal arterioles. In normoxia, in both areas, the pO2 decreased from the inner retina and the choroid towards the middle of the retina. In the inner retina the gradient of the juxta-arteriolar pO2 profile was steeper than that of the intervascular profile. This characteristic persisted during the breathing of 100% O2. Analysis of the pO2 profiles shows that, even in hyperoxia, the choroid cannot supply O2 to the whole retina. The results also support the conclusions of previous work (Riva, Pournaras and Tsacopoulos, 1986) indicating that in the normal retina it is not the O2 diffusing from the choroid to the retinal arterioles the induces vasoconstriction of these vessels. In the miniature pig this constriction appears to maintain inner retina tissue pO2 at a constant level during hyperoxia. From the pO2 transretinal profiles and previously published choroidal O2 fluxes and pO2 values near retinal vessels an explanatory working hypothesis is formulated according to which O2 consumption (qO2) of the outer retina increases during hyperoxia in the miniature pig.

Animals↗
PubMed1989

Developmental expression of the RI subunit of cyclic AMP-dependent protein kinase in retina.

Type I and type II isoenzymes of cyclic AMP-dependent protein kinase were identified by anion exchange chromatography and immunoblotting in human retina at various stages of development. The type I form was typical of the early fetal stage during which proliferation and migration were the primary cellular processes. In later stages of differentiation and maturation, RI was no longer detected: the RII isoform, which appeared at the end of the proliferative phase, being the only isoform seen in mature retina, with a doubling of the specific activity of cyclic AMP-dependent protein kinase. Northern blot analyses showed that an RI transcript of 4.5 kb was present not only in fetal but also in mature human retina. The RI transcript was also found in fetal and adult bovine retina and in adult monkey retina. In vitro translation of mature retinal RNA produced a protein identical in size to authentic RI which was precipitated by anti-RI antiserum. Expression of RI in retina thus appears to be regulated during development. The presence of the mRNA for the RI subunit in the adult retina suggests that the regulation might be post-transcriptional.

Animals↗
PubMed1991

Changes in expression and distribution of lactate dehydrogenase isoenzymes in the developing chick retina.

We have investigated the expression and distribution of lactate dehydrogenase (LDH) isoenzymes in the developing and adult chicken retina. Non-denaturing polyacrylamide gel electrophoresis was used to follow the appearance and expression of the five main LDH isoenzymes in tissue homogenates. Immunohistochemistry was used to define the distribution of the aerobic heart type LDH and the anaerobic muscle type LDH in paraffin sections of embryonic and adult chick retina. The electrophoretic results show that the expression of the anaerobic isoenzyme increases in the retina as development proceeds. Immunoreactivity against the anaerobic isoenzyme localizes to the inner plexiform layer and other regions of the inner chick retina. The aerobic isoenzyme immunoreactivity is localized to the inner segments of the photoreceptor cells as well as the ganglion cell layer. Both antibodies bind weakly in other layers of the retina with the notable exception that the anaerobic protein does not localize in the photoreceptor cell inner segments. These results provide further evidence for the anaerobic nature of the adult inner retina. As retinal development proceeds, the expression of the anaerobic isoenzyme in the retina increases.

Animals↗
PubMed1991

Insulin and IGF-I binding in developing chick neural retina and pigment epithelium: a characterization of binding and structural differences.

We have characterized insulin and insulin-like growth factor I (IGF-I) binding sites in developing chick retina and pigment epithelium (10- and 14-day embryonic, and 2-week post-hatched). For comparison, binding sites in brain and liver were also examined. Both the retina and pigment epithelium (PE) contain separate, specific, high affinity binding sites for insulin and IGF-I. In both tissues, IGF-I binding exceeds insulin binding by two to threefold. Insulin and IGF-I binding in the retina is four to six times greater than in PE. Insulin and IGF-I binding in the retina and PE exhibit independent developmental regulation. In the retina, the number of binding sites decreases by approximately 50% between embryonic day 10 and 2 weeks post-hatching. In the PE, binding decreases slightly between embryonic day 10 and 14 and then, in the 2-week post-hatched chick, increases threefold. Insulin receptor binding subunits in the retina and brain are similar in that both are neuraminidase insensitive and have apparent molecular weights of 116 kD. In contrast, binding subunits in the PE and liver have higher molecular weights (about 126 kD), and are sensitive to neuraminidase. At the embryonic stages examined, the levels of retinal insulin and IGF-I binding exceed those of the brain by five to 13-fold. Taken together, these data suggest that the retina is a major target of insulin and IGF-I and that the binding of these growth factors is developmentally regulated.

Aging↗
PubMed1991

Day and nighttime concentrations of 5-methoxytryptophol and melatonin in the retina and pineal gland from different classes of vertebrates.

5-Methoxytryptophol (ML) and melatonin concentrations were determined by radioimmunoassay in the retinae and pineal glands of frogs (Rana esculenta), chickens (Gallus domesticus), quails (Coturnix coturnix), and European hamsters (Cricetus cricetus), killed in the afternoon (1500-1700 hr) and around midnight (2400-0200 hr). ML was only detectable in significant amounts in the frog retina. In the pineal gland ML levels showed the opposite profile to retinal ML, with measurable levels in the chicken, quail, and hamster and undetectable levels in the frog (less than 2.0 pg/gland). A significant day/night variation was observed in the bird pineal only, with higher levels occurring during the day. In contrast to ML, the interspecies variation in melatonin content was similar in the retina and pineal, with the highest concentrations occurring in the chicken greater than quail much greater than frog greater than hamster. Significantly higher night levels of melatonin were observed in the retina of the chicken and quail and in the pineal of the chicken, quail, and frog. The ratio of ML:melatonin concentrations in the retina and pineal also showed interspecies variations. In the birds the amount of ML was minimal in comparison with the amount of melatonin (1-4% retina; 0.3-12% pineal). The highest ML:melatonin occurred in the retina of the frog and in the pineal of the European hamster.

Animals↗
PubMed1994

The c-wave of the electroretinogram possesses a third component from the proximal retina.

ERG and light-induced extracellular potassium ([K+]o) changes have been measured in isolated retinas of both Rana esculenta and Rana temporaria. The conditions of the preparations have been varied. Isolated frog retinas kept receptor side-upward in a moist chamber without perfusion showed the well-known slow PIII in the ERG. Retinas superfused from the receptor side, with O2 enrichment at their vitreal surface, however, exhibit a slow cornea-positive potential in the ERG. The slow ERG-potentials relate to different light-induced potassium changes in the proximal retina. There was a long lasting and larger proximal potassium increase in adequately maintained retinas but a smaller and shorter one in preparations lacking superfusion and oxygen. There was no significant difference between the size of potassium decrease around receptors of retinas superfused from their vitreal side and those superfused from receptor side. A reduction of slow PIII should therefore not be responsible for the slow cornea-positive potential. The long lasting and larger (by 59%) potassium increase in the proximal retina may counteract the potential in the Müller cells caused by the potassium decrease around receptors and thereby cancel slow PIII and generate a third component of the electroretinogram c-wave.

Animals↗
PubMed1996

Measurement of purine nucleoside concentration in the intact rat retina.

Adenosine, produced from the decomposition of adenosine triphosphate, is believed to provide protective effects during ischemia. On the other hand, adenosine metabolites may serve as precursors for oxygen free radical formation. These substances have not been previously measured in intact vertebrate retina, where adenosine and its metabolites may play a role in the pathogenesis of ischemic injury. The small tissue mass of the retina, particularly in rats, renders these measurements challenging. Furthermore, accurate measurement of purine nucleosides requires immediate cessation of ongoing adenosine metabolism. Concentrations of adenosine and its purine nucleoside metabolites inosine, hypoxanthine, and xanthine in the retina of ketamine/xylazine-anesthetized rats were measured after in situ freezing using high-performance liquid chromatography. The retina was removed from the frozen eyes and analyzed. Quantitative measurements were made possible through the use of an internal standard. Ischemia was induced by ligation of the central retinal artery. Retinal purine nucleoside concentrations did not differ between the two eyes of the rat under control conditions, and there was no effect of placement of the ligating suture itself compared to completely unmanipulated eyes. Use of two different in situ freezing methods yielded comparable results. To evaluate the impact of a period of ischemia, one retina of each rat was ischemic for 30 min, and the other, non-ischemic. Our measurements were associated with a high degree of reproducibility and minimal variability, and significant changes in purine nucleoside concentrations were detectable in the retina after 30 min of ischemia. Our method may be used to assess the role of adenosine and its metabolites in the pathogenesis of ischemic neuronal injury, including in the retina.

Animals↗
PubMed1984

Biosynthesis of gangliosides in cultured retina from chick embryos.

Retina tissue from 7-day chick embryos was maintained in culture for up to 10 days. After 5 days in culture the incorporation of [3H]leucine into proteins and of [3H]glucosamine into gangliosides was similar to that found in retinas from 12-day embryos. The incorporation of [3H]thymidine into DNA decreased steadily with time in culture; after 5 days it was about 20% of the initial value and approximately twice that determined in retinas from 12-day embryos. The radioactivity pattern of gangliosides labeled with [3H]glucosamine showed a predominance of the label in disialosyllactosylceramide (GD3); up to the 3rd day of culture. From then on, there was a progressive increase in the labeling of disialosylgangliotetraosylceramide (GD1a); by day 7 of culture, labeling of GD1a predominated and the labeling pattern was indistinguishable from that found in retinas from 12-day-old embryos. The specific activities of the CMP-NeuAc:GM3 sialosyl- and UDP-GalNAc:GM3 N-acetylgalactosaminyl-transferases decreased to 15% and increased to 400%, respectively, of the values determined in the retinas of 7-day embryos. The cultured retinas progressed in their organization into layers with culture time. The labeling transition from GD3 to GD1a was also detected after inhibition of the histotypic organization by addition of 5-bromo 2-deoxyuridine to the culture medium. Results suggest that high activity of GM3:sialosyl transferase and high labeling of GD3 are associated with the proliferative state of retina cells, while high activity of GM3:N-acetylgalactosaminyltransferase and high labeling of GD1a are associated with the non-proliferative, differentiated state of these cells.

Animals↗
PubMed1991

Development of choline acetyltransferase-immunoreactive neurons in normal and intracranially transplanted retinas in rats.

Retinas from embryonic day 14 (E14) Sprague-Dawley rats were transplanted to the tectum of newborn (P0) recipient rats, and the distribution pattern of choline acetyltransferase immunoreactivity (ChAT-I) in developing transplants was studied and compared with those observed in the retinas of normal developing rats. In normal retinas, ChAT-I cells were first identified in restricted regions in the ganglion cell layer (GCL) at P4, but were found to cover the entire GCL by P6. A second population of ChAT-I cells was detected in the inner nuclear layer (INL) at P8, and they were observed in most parts of the INL on P10 when two immunoreactive sublaminae began to appear in the inner plexiform layer (IPL). The adult pattern of having two distinct populations of ChAT-I cells, organized in mirror symmetrical fashion in the inner retinal layers was basically established by P12. The time course of development and overall distribution pattern of ChAT-I cells in developing retinal transplants on the whole were very similar to those observed in normal retinas. The first identification of these cells and the establishment of their final distribution pattern were made at stages corresponding to P4 and P12 of normal developing retinas respectively. However, ChAT-I somata were located in the INL at a much earlier stage compared with their counterparts in the normal retina, and a transient population of immunoreactive cells with their processes extending to retinal layers other than the IPL was observed in some transplants from P6 to P10. These features were not observed in normal developing retinas. These results suggest that the development of cholinergic neurons, especially the expression of their characteristic antigen and their final distribution pattern is largely determined by programmes which are intrinsic to the original retinal tissue, despite some minor deviation or variation in the developmental process which may occur under certain abnormal conditions.

Animals↗
PubMed1988

An antiserum against chicken hydroxyindole-O-methyltransferase reacts with the enzyme from pineal gland and retina and labels pineal modified photoreceptors.

Biosynthesis of the indolic hormone melatonin has been reported in the pineal gland and retina. The terminal step of melatonin synthesis is catalysed by hydroxyindole-O-methyltransferase (HIOMT), an enzyme displaying highest levels of activity in the pineal gland and retina. Several laboratories have suggested that melatonin synthesis might take place in retinal photoreceptors and in photoreceptor-derived cells of the pineal gland. Experimental support to this hypothesis is progressively building up with the immunocytochemical identification of HIOMT-containing cells in various animal species. In the present report, HIOMT was purified from the chicken pineal gland using a one-step chromatographic procedure and an antiserum against the enzyme was obtained in the rabbit. The antiserum was further purified by immunoadsorption chromatography on chicken brain proteins. Using electroblots immunochemical labeling, HIOMT from chicken pineal gland and retina was identified as a 38-kDa protein. Pineal HIOMT was further resolved into components of different pHi-values (5.4-5.7 and 6.8), using two-dimensional gel electrophoresis. Immunoprecipitation of HIOMT activity was observed in pineal homogenates and, for the first time, in homogenates of the retina. Immunofluorescence microscopy provided the first evidence that HIOMT is contained in modified photoreceptors of the chicken pineal gland. No immunofluorescence could be observed in the retina, maybe due to the lower level of HIOMT activity in this tissue. Together, the data indicate that the antiserum may be a useful tool to study the regulation of HIOMT synthesis in the pineal gland and in the retina. Further work is required to identify HIOMT-containing cells in the retina.

Acetylserotonin O-Methyltransferase↗
PubMed1996

Characterization of [2-3H]deoxy-D-glucose uptake in retina and retinal pigment epithelium of normal and diabetic rats.

The outer blood-retinal barrier which results from the tight junctions between retinal pigment epithelial cells (RPE) restricts the flow of nutrients reaching the retina. We characterize the transport of [2-3H]deoxy-D-glucose (2-DG) across isolated mammalian neural retina and RPE in terms of their kinetics constants. In addition, the effect of insulin on glucose transport was studied by using streptozotocin-induced diabetic rats. RPE accumulates 2-DG by a temperature-sensitive and energy-dependent complex kinetics mechanism. The retina takes up 2-DG by an energy and Na(+)-dependent saturable system with an apparent Km of 2 mM. Insulin induced an increase of 2-DG uptake by normal retina. The retina of diabetic rats shows lower levels of 2-DG accumulation. These levels can be returned to the normal ones by exposure to insulin. Although insulin does not affect, significantly, 2-DG accumulation by RPE, 2-DG uptake of RPE from diabetic rats shows a normal saturable kinetics with an apparent Km of 20 mM. Those findings suggest the presence of different types of glucose transporters in retina and RPE. Insulin-sensitive glucose transport in retina might be involved in the manifestation of diabetic retinopathy.

Animals↗
PubMed1996

Thyrotropin-like immunoreactivity in human retina: immunoreactive co-localization in ganglion cells and perivascular fibers.

The present immunocytochemical study has demonstrated immunoreactive thyrotropin-like ganglion cell populations as well as perivascular fibers in the human retina by using specific antiserum. Thyrotropin is a pituitary glycopeptide involved in the synthesis and release of thyroid hormones. The existence and functions of peptides in vertebrate retinas are still not well known. Many authors have reported neuropeptide immunoreactivity in the human retina which have had their functions established in the neuroregulatory processes of vision. Moreover, some authors have reported the possibility that the fiber terminal of peptidergic neurons may also be a blood vessel. The appearance of immunoreactive-cells in human retina, e.g. existence of retinal ganglion cells with thyrotropin-like immunoreactivity, indicates the existence of specific mechanisms that would be mediated by these peptides which are located near immunoreactive ganglion cells. We hypothesize that there is an intrinsic mechanism for blood flow control, mediated by retinal ganglion cells which may regulate vessel diameter according to its luminous stimuli. No-one has demonstrated the presence or the functional existence of thyrotropin-like immunoreactive structures in the vertebrate retina, or on the side of the pituitary-thyroid axis. To the best of our knowledge this is the first time that thyrotropin has been immunocytochemically demonstrated in the human retina. Thus, we suggest that thyrotropin acts as a neuromodulator in the human retina, which is implicated in blood flow control.

Animals↗
PubMed1994

Vasoactive intestinal polypeptide/peptide histidine isoleucine messenger RNA in the rat retina: adult distribution and developmental expression.

In the adult nervous system, vasoactive intestinal polypeptide acts as a neurotransmitter or neuromodulator, and during development, it may also act as a neurotrophic factor. In the adult mammalian retina, this peptide is contained in a population of wide-field amacrine cells. Using in situ hybridization histochemistry, we examined the distribution and developmental expression of vasoactive intestinal polypeptide/peptide histidine isoleucine messenger RNA in the rat retina. Retinas collected from birth to adulthood were hybridized with an RNA probe as whole mounts, and then cut either perpendicular or parallel to the vitreal surface. Adult retinas were used in double labeling experiments for the visualization of both the hybridization signal and vasoactive intestinal polypeptide immunoreactivity in the same tissue section. In adult retinas, vasoactive intestinal polypeptide/peptide histidine isoleucine messenger RNA is localized to amacrine cells positioned in the proximal inner nuclear layer, and rarely to displaced amacrine cells in the inner plexiform layer and ganglion cell layer. The neurons expressing this messenger RNA are sparsely distributed, with a non-random distribution and densities of about 190 cells/mm2. An estimate of their total number gives about 12,350 cells/retina. The double labeling experiments showed that the hybridization signal is specifically confined to neurons displaying vasoactive intestinal polypeptide immunoreactivity. Vasoactive intestinal polypeptide/peptide histidine isoleucine messenger RNA is first detected at postnatal day 5 in cells located in the proximal part of the neuroblastic layer. A greater number of these neurons is present in the inner nuclear layer at postnatal day 10, and a few labeled neurons are also detected in the inner plexiform layer and in the ganglion cell layer. At this time, vasoactive intestinal polypeptide/peptide histidine isoleucine messenger RNA-containing amacrines in the inner nuclear layer are non-randomly distributed on the retinal surface, as in adult retinas. At postnatal day 15 (eye opening), there is a peak in both the density and the estimated number of labeled neurons, and their pattern of distribution in the retinal layers is similar to that in the adult. The present study shows that in the adult rat retina vasoactive intestinal polypeptide and peptide histidine isoleucine are synthesized in a sparsely distributed amacrine cell population, extending previous immunohistochemical findings. The appearance of vasoactive intestinal polypeptide peptide histidine isoleucine messenger RNA during the first postnatal week is consistent with the reported appearance of other transmitter-identified amacrine cell populations.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Role of N-cadherin cell adhesion molecules in the histogenesis of neural retina.

We investigated the role of N-cadherin cell adhesion molecules in the histogenesis of the chicken neural retina. In the undifferentiated retina of early embryos, N-cadherin is almost evenly distributed. With differentiation, N-cadherin was gradually localized in particular cell layers. In the 8.5 to 10.5 day embryos, N-cadherin was most abundant in the optic nerve fiber layer, the plexiform layers and the outer limiting membrane. Thereafter, this molecule gradually diminished from most parts of the retina, except in the outer limiting membrane. When incubated with Fab fragments of a polyclonal antibody to N-cadherin, retinas of early embryos tended to dissociate and could not be maintained as a tissue mass. Retinas from older embryos were not dissociated by the Fab, but their morphogenesis was severely affected. We conclude that N-cadherin is essential for maintaining the overall structure of the undifferentiated retina, but during development, its role becomes restricted to maintaining more specific regions of the tissue. We also suggest that there might be additional, unidentified cadherin-like molecules in the retina.

Animals↗
PubMed2003

Caloric restriction retards age-related changes in rat retina.

The neural retina of mammals consists of light sensitive photoreceptors and connecting neural cells that receive and send visual signal to the brain. Dietary caloric restriction (CR) is the only experimental intervention that can reliably retard the age-related degeneration of the retina in a normal mammalian model. Here, we studied the effect of CR on various biochemical parameters in the retina of male Brown Norway rats at different ages. We found that CR slowed the age-dependent protein insolubilization, blunted the declines in the total soluble thiols, and reduced glutathione and ascorbic acid levels in neural retina. We also observed that CR retarded the age-related decline in the levels of taurine, a vital amino acid in neural retina. These data are the first to implicate that CR may retard the age-related degeneration of retina by attenuating the oxidative stress and/or by sustaining the pool of protective factors in the neural retina.

Aging↗
PubMed2004

Microglial responses in the avascular quail retina following transection of the optic nerve.

This study was undertaken to investigate microglial responses in the avascular central nervous system using the quail retina that is known to be devoid of blood vessels. Following intraorbital optic nerve transection (ONT), the quail retina was examined immunohistochemically at various times up to 6 months. A few days after transection, microglia in the inner retinal layers revealed features of activation. Activated cells displayed an amoeboid shape and enhanced QH1-immunoreactivity. The numbers of these amoeboid cells were rapidly increased, first in the inner plexiform layer (IPL), and then in the ganglion cell/nerve fiber layer (GCL/NFL) of the retina where retrograde degenerating ganglion cell processes and perikarya were located. By 6 months after transection, microglia regained their resting morphology, and their cell counts returned to control levels. At early time points of microglial activation, numerous QH1+ amoeboid cells were observed along the vitreal surface of the pecten and retinal region adjacent to the insertion of the pecten, where some amoeboid cells were attached underneath the internal limiting membrane, and appeared to squeeze through the optic nerve fiber bundles. A considerable number of these amoeboid cells in the GCL/NFL and the IPL were labeled with PCNA, suggesting that active exogenous migration (from the pecten) and in situ proliferation of precursor cells contribute to the increase in microglial population of the degenerating retina. On the other hand, TUNEL-positive microglia appeared in the GCL/NFL at later time points indicate that the decrease of microglial numbers is in part due to apoptosis in these layers. Although some aspects of microglial activation in the avascular retina appear unique, their consequences were similar to those described in vascular retinae of mammals, a finding indicates that blood vessels are not a prerequisite for microglial activation, and microglial precursors could migrate long distance to reach the lesioned site, which is not accessible via blood vessels. Our data provide the first analysis of microglial activation in the avascular central nervous system (CNS), and suggest that the quail retina is a useful model for studies of microglial behavior in CNS.

Animals↗