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PubMed1986

Effects of light and darkness on oxygen distribution and consumption in the cat retina.

These experiments were done to investigate the effects of light and darkness on the oxygenation of the retina in anesthetized cats. Measurements were made with double-barreled oxygen microelectrodes capable of recording both oxygen tension (PO2) and local voltages. Diffuse white illumination presented to a dark-adapted retina led to an increase in PO2 of up to 30 mmHg in the outer half of the retina. Changes were maximal at approximately 75% depth, corresponding to the outer nuclear layer. No change or decrease in PO2 was observed in the inner retina. Light-evoked increases in outer retinal PO2 were graded with the duration and strength of illumination, and were maximal in response to 60 s of illumination at rod saturation. For these stimuli, the increase at the onset of illumination was slower (average half-time, 12.2 s) than the recovery at the end of illumination (average half-time, 5.9 s), but for stimuli above rod saturation, PO2 recovered much more slowly. The profile of PO2 was measured during electrode penetration and withdrawal and during light and dark adaptation. Dark-adapted profiles were characterized by a minimum PO2 of nearly 0 mmHg at depths of 65-85%, and a steep gradient from the minimum to the choroid. During light adaptation at rod saturation, PO2 was elevated in the outer half of the retina and the minimum was eliminated. Fits of the profiles to a one-dimensional model of oxygen diffusion indicated that light reduced the oxygen consumption of the outer retina to approximately 50% of its dark-adapted value.

Animals↗
PubMed1992

Oxygen distribution and consumption in the cat retina during normoxia and hypoxemia.

Oxygen tension (PO2) was measured with microelectrodes within the retina of anesthetized cats during normoxia and hypoxemia (i.e., systemic hypoxia), and photoreceptor oxygen consumption was determined by fitting PO2 measurements to a model of steady-state oxygen diffusion and consumption. Choroidal PO2 fell linearly during hypoxemia, about 0.64 mmHg/mmHg decrease in arterial PO2 (PaO2). The choroidal circulation provided approximately 91% of the photoreceptors' oxygen supply under dark-adapted conditions during both normoxia and hypoxemia. In light adaptation the choroid supplied all of the oxygen during normoxia, but at PaO2's less than 60 mmHg the retinal circulation supplied approximately 10% of the oxygen. In the dark-adapted retina the decrease in choroidal PO2 caused a large decrease in photoreceptor oxygen consumption, from approximately 5.1 ml O2/100 g.min during normoxia to 2.6 ml O2/100 g.min at a PaO2 of 50 mmHg. When the retina was adapted to a rod saturating background, normoxic oxygen consumption was approximately 33% of the dark-adapted value, and hypoxemia caused almost no change in oxygen consumption. This difference in metabolic effects of hypoxemia in light and dark explains why the standing potential of the eye and retinal extracellular potassium concentration were previously found to be more affected by hypoxemia in darkness. Frequency histograms of intraretinal PO2 were used to characterize the oxygenation of the vascularized inner half of the retina, where the oxygen distribution is heterogeneous and simple diffusion models cannot be used. Inner retinal PO2 during normoxia was relatively low: 18 +/- 12 mmHg (mean and SD; n = 8,328 values from 36 profiles) in dark adaptation, and significantly lower, 13 +/- 6 mmHg (n = 4,349 values from 19 profiles) in light adaptation. Even in the dark-adapted retina, 30% of the values were less than 10 mmHg. The mean PO2 in the inner (i.e., proximal) half of the retina was well regulated during hypoxemia. In dark adaptation it was significantly reduced only at PaO2's less than 45 mmHg, and it was reduced less at these PaO2's in light adaptation.

Adaptation, Biological↗
PubMed1997

Sulfonamides do not reach the retina in therapeutic amounts after topical application to the cornea.

Retinal drug concentrations were measured in treated and fellow eyes following topical administration of two potent and permeable carbonic anhydrase inhibitors, MK-927 and trifluoromethanesulfonamide (CF3SO2NH2) in the rabbit. Administration of 2 or 5 drops 2% MK-927 or 2% CF3SO2NH2 gave at 1 hr 1.5-9 microM drug in the retinas of treated eyes and 1.3-3.7 microM drug in the retinas of the fellow eye. After allowance was made for the blood content of the retinas (1.4-13%) and drug contained in whole blood due to systemic absorption, little (< 1.4 microM) or no net accumulation in retina could be documented. In a second series of experiments animals were treated with 5 mg/kg i.v. of either MK-927 or CF3SO2NH2 in order to fully saturate red cell carbonic anhydrase prior to topical administration of drug. For MK-927 there was a net accumulation in retina 3 hrs following topical administration in both treated and fellow eyes (3-4 microM) which was approximately 1/4 the concentration in plasma, suggesting that some drug had permeated the blood-retinal barrier. Similar results were obtained with CF3SO2NH2, giving no difference between treated and fellow eyes; retinal concentrations were approximately 90% of plasma concentrations. These results suggest that there is no direct access to retina by posterior or uveoscleral drainage of topically applied sulfonamides other than systemically absorbed drug.

Administration, Topical↗
PubMed1998

Influence of destruction of retina-RPE complex on the proliferation of scleral chondrocytes in chicks.

We studied the role of the retina-retinal pigment epithelium (RPE) complex in the proliferation of scleral chondrocytes in chicks. Seventy-two chicks were allocated to one of four groups: intravitreal gentamicin (400 microg) injection (destruction of retina-RPE complex); intravitreal gentamicin injection with goggling; goggling only (form-deprivation myopia); and intravitreal saline injection (control). The chicks were killed and retina-RPE complexes were harvested under a microscope. Retina-RPE complexes were then co-cultured with primary culture of first day scleral chondrocytes in Transwell-COL co-culture systems (Costar), with two different pore sizes (0.4 and 3.0 microm) and serum-deprivation medium. An MTT assay was performed at A550 after 4 days. In the 0.4 microm pore size system, the absorbency at A550 showed no differences between groups. However, in the 3.0 microm pore size system, the absorbency at A550s in the intravitreal gentamicin groups was significantly lower than in the control and the goggle groups (p<0.05), indicating that destruction of the retina-RPE complex inhibited chondrocyte proliferation. The absorbency in the goggle group was higher than in the control group (p<0.05). These results indicate that the retina-RPE complex exerts a positive effect on the proliferation of scleral chondrocytes via a molecule sized between 0.4.and 3.0 microm in diameter.

Animals↗
PubMed1997

Dp260 disrupted mice revealed prolonged implicit time of the b-wave in ERG and loss of accumulation of beta-dystroglycan in the outer plexiform layer of the retina.

Dp260 is a C-terminal isoform of dystrophin and is expressed specifically in the retina. Abnormal electroretinograms (ERG) in some Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) patients are likely linked to a disruption of Dp260. To clarify the importance of Dp260 in the retina, we examined dystrophin exon 52 knock-out mice, whose expression of Dp260 is impaired. We also confirmed the localization of Dp260 in the outer plexiform layer (OPL) of the retina. Disruption of Dp260 causes a change in the localization of beta-dystroglycan, which is normally found in the OPL of the retina. This suggests a requirement for Dp260 for normal formation of the dystrophin-dystroglycan complex in the retina. Dp71, also expressed in the retina, was, however, not detected in the OPL. The difference in localization of Dp260 and Dp71 implies that the two isoforms have different functions. The dystrophin exon 52 knock-out mice had a prolonged implicit time of the b-wave in ERG, although no significant change was observed in amplitude. These ERG findings differed from those of DMD and BMD patients, especially with regard to amplitude of the b-wave, but make it clear that Dp260 is required for normal electrophysiology.

Animals↗
PubMed2005

Identification of regulatory targets of tissue-specific transcription factors: application to retina-specific gene regulation.

Identification of tissue-specific gene regulatory networks can yield insights into the molecular basis of a tissue's development, function and pathology. Here, we present a computational approach designed to identify potential regulatory target genes of photoreceptor cell-specific transcription factors (TFs). The approach is based on the hypothesis that genes related to the retina in terms of expression, disease and/or function are more likely to be the targets of retina-specific TFs than other genes. A list of genes that are preferentially expressed in retina was obtained by integrating expressed sequence tag, SAGE and microarray datasets. The regulatory targets of retina-specific TFs are enriched in this set of retina-related genes. A Bayesian approach was employed to integrate information about binding site location relative to a gene's transcription start site. Our method was applied to three retina-specific TFs, CRX, NRL and NR2E3, and a number of potential targets were predicted. To experimentally assess the validity of the bioinformatic predictions, mobility shift, transient transfection and chromatin immunoprecipitation assays were performed with five predicted CRX targets, and the results were suggestive of CRX regulation in 5/5, 3/5 and 4/5 cases, respectively. Together, these experiments strongly suggest that RP1, GUCY2D, ABCA4 are novel targets of CRX.

Animals↗
PubMed1988

Dopaminergic neurons in the cat retina.

Dopaminergic neurons have been directly visualized in the flat mount cat retina with an immunohistochemical technique that uses antisera directed to the enzyme tyrosine hydroxylase. In a previous study, three specific neuronal populations--amacrine cells, displaced amacrine (DA) cells, and interplexiform (IP) cells--were identified on the basis of morphology in the flat mount retina. The present study incorporates three-dimensional computer reconstructions and differences in the frequency distributions of some area to support the original cell classification. The three neuronal populations differ in cell numbers and spatial distributions in the retina; quantitative comparison of two cat retinas shows that the total numbers of cells and the spatial distributions of the three cell populations are consistent between retinas. These results suggest that a single neurotransmitter can serve different functions in modifying signals and flow of visual information within the neural networks of the retina.

Animals↗
PubMed2004

Effects of endothelin-1 eyedrops on the retina in rats.

Eye disorder accompanied with chronic retinal microvascular obstruction, such as diabetic retinopathy, exists in many diseases. However, it is difficult to produce this model experimentally in the animal eye. Endothelin-1 eyedrops were prepared in order to examine whether the eyedrops affect the rat retina and whether we can produce an obstruction model. Endothelin-1 eyedrops diluted by artificial tears in seven stages from 4 x 10(-5) M to 4 x 10(-11) M were arranged. We administered this solution three times a day in the left eye of male Sprague-Dawley rats. Artificial tears alone were applied to the right eye as a control vehicle. After 2 weeks, rats were sacrificed under anesthesia and the retinal tissues were isolated. As an index to the action of endothelin- 1 eyedrops to the retina, the expressions of endothelin-A (ETA) and endothelin-B (ETB) receptors in the retina were compared in both eyes. Frozen sections of the retina were immunostained to reveal the distribution of the ETA and ETB receptors. We also examined ETA and ETB mRNA expression by quantitative real-time polymerase chain reaction. As a result, the expressions of ETA and ETB receptors are reduced with both immunostaining and the mRNA levels in the left eye, in which endothelin-1 eyedrops were applied at 4 x 10(-5) M. It is suggested that endothelin-1 eyedrops affected the retina and the possibility of producing the experimental model of chronic microvascular obstruction in the rat retina.

Administration, Topical↗
PubMed1984

The functions of acetylcholine in the rabbit retina.

Rabbit retinas were incubated in vitro under conditions known to maintain their physiological function. The acetylcholine stores of the cholinergic amacrine cells were labelled by incubation in the presence of [3H]choline. The tissue was then mounted in a fast-flow superfusion chamber, and the release of [3H]acetylcholine under various conditions was measured by liquid cation exchange or high-voltage electrophoresis. When the retina was stimulated by flashing light, the rate of appearance of radioactive acetylcholine in the superfusate increased, with a latency shorter than the resolution of the system. The rate of release of acetylcholine remained elevated as long as the light was flashing, and returned rapidly to baseline when the light was extinguished. A one minute stimulation with steady light caused a burst of acetylcholine release following stimulus onset and a second, smaller, burst following stimulus cessation. In the presence of 2-amino-4-phosphonobutyrate (APB), an agent known to eliminate selectively the transmission of ON responses to the proximal retina, steady light caused acetylcholine release only at stimulus cessation. Other retinas were labelled with [3H]choline, then incubated for 10-80 min in the presence of flashing light (to promote acetylcholine release) and either control medium or medium containing 100 micron APB (to prevent release from cells activated by stimulus onset). These retinas were quick-frozen, freeze-dried and radioautographed on dry emulsion. In retinas incubated under control conditions [3H]acetylcholine was initially present within two bands within the inner plexiform layer. The two bands became fainter together as the tissue's [3H]acetylcholine was released. APB selectively retarded the depletion of [3H]acetylcholine from the band nearest the ganglion cell layer. We conclude that the displaced cholinergic amacrine cells release acetylcholine at the transient when light appears, and the conventionally placed cholinergic amacrine cells release acetylcholine at the transient when light is extinguished. The retinal ganglion cells that receive a light-driven cholinergic input are distinguished from those that do not by a great sensitivity to slow stimulus motion. It is proposed that the dense plexus of cholinergic dendrites and the transient nature of acetylcholine release combine to create the local subunit that enables detection of motion within regions smaller than those ganglion cells' receptive fields.

Acetylcholine↗
PubMed1982

The morphology of the bipolar cells, amacrine cells and ganglion cells in the retina of the turtle Pseudemys scripta elegans.

The morphology of the neurons that contribute to the inner plexiform layer of the retina of the turtle Pseudemys scripta elegans has been studied by light microscopy of whole-mount material stained by the method of Golgi. Cells have been distinguished on the basis of criteria that include dendritic branching patterns, dendritic morphology, dendritic tree sizes and stratification of processes in the inner plexiform layer. Many of the neurons have dendritic trees oriented parallel to and a few exhibit an orthogonal orientation with the linear visual streak present in the retina of this species. The neurons of the turtle retina have been compared, where possible, with the neurons of the lizard retina as described by Cajal. The findings are discussed in relation to other vertebrate retinas, and correlations are made with recent electrophysiological recordings of the turtle retina. Comments are made with regard to the significance of orientation of neurons relative to the linear visual streak.

Action Potentials↗
PubMed2000

Light-adaptive role of nitric oxide in the outer retina of lower vertebrates: a brief review.

The role of nitric oxide (NO) as a novel neurochemical mechanism controlling light adaptation of the outer retina is discussed by considering mainly published results. The emphasis is on the retinae of fishes and amphibia, but some data from the mammalian (rabbit) retinae have also been included for completeness. In the fish retina, application of NO donors in the dark caused light-adaptive photomechanical movements of cones. The normal effect of light adaptation in inducing cone contractions was suppressed by pretreatment of retinae with an NO scavenger. NO donors modulated horizontal cell activity by uncoupling the cells' lateral gap junctional interconnections and enhancing negative feedback to cones, again consistent with a light-adaptive role of NO. Direct evidence for light adaptation-induced release of NO has been obtained in fish (carp) and rabbit retinae. The results strongly suggest that control of retinal light adaptation is, under multiple neurochemical control, with NO and dopamine having an interactive role.

Adaptation, Physiological↗
PubMed2004

Optic nerve signals in a neuromorphic chip I: Outer and inner retina models.

We present a novel model for the mammalian retina and analyze its behavior. Our outer retina model performs bandpass spatiotemporal filtering. It is comprised of two reciprocally connected resistive grids that model the cone and horizontal cell syncytia. We show analytically that its sensitivity is proportional to the space-constant-ratio of the two grids while its half-max response is set by the local average intensity. Thus, this outer retina model realizes luminance adaptation. Our inner retina model performs high-pass temporal filtering. It features slow negative feedback whose strength is modulated by a locally computed measure of temporal contrast, modeling two kinds of amacrine cells, one narrow-field, the other wide-field. We show analytically that, when the input is spectrally pure, the corner-frequency tracks the input frequency. But when the input is broadband, the corner frequency is proportional to contrast. Thus, this inner retina model realizes temporal frequency adaptation as well as contrast gain control. We present CMOS circuit designs for our retina model in this paper as well. Experimental measurements from the fabricated chip, and validation of our analytical results, are presented in the companion paper [Zaghloul and Boahen (2004)].

Action Potentials↗
PubMed2006

An analog silicon retina with multichip configuration.

The neuromorphic silicon retina is a novel analog very large scale integrated circuit that emulates the structure and the function of the retinal neuronal circuit. We fabricated a neuromorphic silicon retina, in which sample/hold circuits were embedded to generate fluctuation-suppressed outputs in the previous study [1]. The applications of this silicon retina, however, are limited because of a low spatial resolution and computational variability. In this paper, we have fabricated a multichip silicon retina in which the functional network circuits are divided into two chips: the photoreceptor network chip (P chip) and the horizontal cell network chip (H chip). The output images of the P chip are transferred to the H chip with analog voltages through the line-parallel transfer bus. The sample/hold circuits embedded in the P and H chips compensate for the pattern noise generated on the circuits, including the analog communication pathway. Using the multichip silicon retina together with an off-chip differential amplifier, spatial filtering of the image with an odd- and an even-symmetric orientation selective receptive fields was carried out in real time. The analog data transfer method in the present multichip silicon retina is useful to design analog neuromorphic multichip systems that mimic the hierarchical structure of neuronal networks in the visual system.

Algorithms↗
PubMed1979

The development of inducibility for glutamine synthetase in embryonic neural retina: inhibition by BrdU.

The hydrocortisone-mediated induction of glutamine synthetase (GS) in the neural retina of the chick embryo is a characteristic and unique feature of differentiation of this tissue. The induction involves genomic activity elicited by the inducer resulting in synthesis and accumulation of the enzyme. We describe correlations between the growth of embryonic retina tissue in vivo and in vitro and the development of its inducibility for GS, and demonstrate that this development proceeds through two phases: competence-acquisition phase (before the 7th day of development), and maturation phase. BrdU applied for 24 h to retinas of 5-day embryos irreversibly suppresses the development of induction-competence. However, BrdU does not affect the progressive maturation of inducibility when applied to retinas that already are fully induction-competent (8 days and older). The short treatment with BrdU of 5-day retinas also causes defective histogenesis resulting in drastic malformation of the tissue. The nature of the processes involved in competence-acquisition and in the maturation of inducibility for GS are examined. Possible mechanisms by which BrdU prevents the development of induction-competence for GS in the early embryonic retina and elicits defective histogenesis are discussed.

Animals↗
PubMed1983

The pattern of DNA methylation in the delta-crystallin genes in transdifferentiating neural retina cultures.

Terminally differentiated lens fibre cells are formed in the vertebrate lens throughout life. Lens fibre cells may also be obtained by an in vitro process termed transdifferentiation, from certain tissues of different developmental origin from lens, such as embryo neural retina. delta-Crystallin is the major protein in the chick embryo lens fibre cells, and also in transdifferentiated lens cells obtained from cultured embryonic neural retina. Lens crystallin proteins and mRNA are present at low levels in the intact embryonic neural retina but are no longer detectable in the early stages of neural retina cell culture. However, levels rise steeply in the later stages and crystallins become the major products in terminally transdifferentiating neural retina cultures. We have used this system to test the hypothesis that the patterns of DNA methylation in particular genes are correlated with gene expression. A number of developmentally regulated genes have been found to be undermethylated in tissues where they are expressed, and methylated in tissues where they are not. However this correspondence does not always hold true. Eight-day-old embryonic neural retina was cultured for the period of time during which crystallin gene expression increases 100-fold. DNA methylation in the delta-crystallin gene region was analysed at several stages of cell culture by using the restriction endonucleases HpaII and MspI which cleave at the sequence CCGG. The former enzyme cannot cleave internally methylated cytosine (CmCGG) while the latter cannot cleave externally methylated cytosine (mCCGG). We detect no change in the methylation of CCGG sites within the delta-crystallin gene regions during transdifferentiation. Since dramatic changes in delta-crystallin gene expression occur during this process we conclude that large scale alterations in the pattern of DNA methylation are not a necessary accompaniment to changes in gene activity.

Animals↗
PubMed2005

The presence of megamitochondria in the ellipsoid of photoreceptor inner segment of the zebrafish retina.

Although the megamitochondria (MM) were localized in various pathological conditions, normal retina of some mammalian species was reported to include MM for various physiological roles. However, it was not clearly confirmed whether the MM is present in the retina of lower vertebrate as well. In this study, we tried to show the presence of the MM in the zebrafish retina using electron microscopic technique. In all the photoreceptors including rods, cones and double cones of the zebrafish retina, MM were observed in the ellipsoid of inner segment. In the photoreceptor epllipsoid of the zebrafish retina, the mitochondria located in the central portion of the ellipsoid had a highly electron-dense matrix, which were accompanied by the mitochondria with electron-lucent matrix in the apical portion of the ellipsoid. The presence of MM was more clearly discernable in the rods, which were localized under the double cones. This finding is somewhat different from those observed in the previous studies because MM were localized in the inner segment of cones, but were not in those of rods in the case of mammalian retina. Although the exact physiological meaning for the presence of MM in some vertebrate species should be further studied, the present study could show that the MM in the ellipsoid of the retinal photoreceptors was not only restricted in some mammalian species.

Animals↗
PubMed1993

Acidic fibroblast growth factor is expressed abundantly by photoreceptors within the developing and mature rat retina.

In order to further understand the role(s) of fibroblast growth factors (FGFs) in the development, differentiation and function of the central nervous system, we analysed the expression of the mRNA, and the presence and tissue distribution of the translated product, of one member of the FGF family, acidic FGF (aFGF), within the mammalian retina. Firstly, the relative abundance of aFGF mRNA was assayed in embryonic (between 14 and 17 days of gestation), postnatal (between 1 and 17 days after birth) and adult rat retina by quantitative reverse transcription-coupled polymerase chain reaction amplification using specific aFGF oligonucleotides. The level of expression remained uniformly low throughout the embryonic period and until postnatal day 7. Therefore the quantity of aFGF mRNA increased rapidly, reaching 80% of adult levels by eye opening (postnatal day 13). Adult levels were three-fold higher than at early developmental times. In situ hybridization of adult rat retina using specific antisense aFGF riboprobes revealed labelling in all cellular layers. Antisera raised against recombinant human aFGF revealed very little labelling of 4-day postnatal retina, but by postnatal days 8 and 17 immunoreactive aFGF was localized mainly within the photoreceptor cell bodies. Western blots of retinal extracts derived from 17-day embryonic, 4-day postnatal and adult retina probed with the same antibody revealed a single immunoreactive band of the expected molecular weight (18 kDa) in all extracts. Thus aFGF is mostly transcribed and translated within the retina subsequent to the major steps of cell birth, migration and differentiation, and seems to be abundantly expressed by maturing photoreceptor cells.

Animals↗
PubMed1982

Adenosine-elicited accumulation of adenosine 3', 5'-cyclic monophosphate in the chick embryo retina.

The cyclic AMP level of 17-day-old chick embryo retina increased from 20 to 331 pmol/mg protein when the tissue was incubated for 20 min in the presence of 4-(3-butoxy-4-methoxybenzyl-2-imidozolinone) (RO 20-1724). The addition of 0.5 mM-3-isobutyl-1-methylxanthine (IBMX) or 0.5 units/ml of adenosine deaminase (EC 3.5.4.4) to the medium reduced the increase of cyclic AMP content from 20 to 100 pmol/mg protein. Dipyridamole did not interfere with the rise of the retinal cyclic AMP level observed with RO 20-1724. The EC50 of 6-amino-2-chloropurine riboside (2-chloroadenosine)-elicited accumulation of cyclic AMP of retinas incubated in the presence of RO 20-1724 plus adenosine deaminase was approximately 1 microM. When retina incubation was carried out in the presence of 0.5 mM-IBMX, the 2-chloroadenosine dose-response curve was shifted to the right two orders of magnitude. Maximal stimulation of the cyclic AMP level of 17-day-old chick embryo retina incubated in the presence of 0.5 mM-IBMX was observed at 1 mM-adenosine concentration. This effect was not blocked by dopamine antagonists. Guanosine and adenine did not affect the retinal cyclic AMP level. AMP and ATP had a slight stimulatory effect. Adenosine response of embryonic retina increased sharply from the 14th to the 17th embryonic day. A similar, but not identical adenosine effect was observed in cultured retina cells.

1-Methyl-3-isobutylxanthine↗