Correlations between Photodegradation of Bisretinoid Constituents of Retina and Dicarbonyl Adduct Deposition

Non-enzymatic collagen cross-linking and carbonyl adduct deposition are features of Bruch''s membrane aging in the eye, and disturbances in extracellular matrix turnover are considered to contribute to Bruch''s membrane thickening. Because bisretinoid constituents of the lipofuscin of retinal pigment epithelial (RPE) cells are known to photodegrade to mixtures of aldehyde-bearing fragments and small dicarbonyls (glyoxal (GO) and methylglyoxal (MG)), we investigated RPE lipofuscin as a source of the reactive species that covalently modify protein side chains. Abca4^−/− and Rdh8^−/−/Abca4^−/− mice that are models of accelerated bisretinoid formation were studied and pre-exposure of mice to 430 nm light enriched for dicarbonyl release by bisretinoid photodegradation. MG protein adducts were elevated in posterior eyecups of mutant mice, whereas carbonylation of an RPE-specific protein was observed in Abca4^−/− but not in wild-type mice under the same conditions. Immunolabeling of cryostat-sectioned eyes harvested from Abca4^−/− mice revealed that carbonyl adduct deposition in Bruch''s membrane was accentuated. Cell-based assays corroborated these findings in mice. Moreover, the receptor for advanced glycation end products that recognizes MG and GO adducts and glyoxylase 1 that metabolizes MG and GO were up-regulated in Abca4^−/− mice. Additionally, in acellular assays, peptides were cross-linked in the presence of A2E (adduct of two vitamin A aldehyde and ethanolamine) photodegradation products, and in a zymography assay, reaction of collagen IV with products of A2E photodegradation resulted in reduced cleavage by the matrix metalloproteinases MMP2 and MMP9. In conclusion, these mechanistic studies demonstrate a link between the photodegradation of RPE bisretinoid fluorophores and aging changes in underlying Bruch''s membrane that can confer risk of age-related macular degeneration.     

Ethanolamine Accumulation by Photoreceptor Cells of the Rabbit Retina

The rabbit retina accumulates ethanolamine by an overall process that has a high affinity for ethanolamine. This process is different from the choline uptake, since ethanolamine accumulation was unaffected by high choline concentrations. Autoradiography identified the major site of high-affinity uptake as the perinuclear region of the photoreceptor cells. Ethanolamine accumulated by the high-affinity uptake was not used for neurotransmission by photoreceptor cells but was used to synthesize phosphatidylethanolamine. However, only a small percentage of the accumulated ethanolamine was converted into phospholipid. The rate of phosphorylation may contribute to control of phospholipid synthesis, since choline kinase activity is much greater than ethanolamine kinase activity in the rabbit retina.     

Cytochemical Alterations in the Rat Retina by LPS Administration

LPS-induced inflammation and changes in protein phosphorylation and the JAK-STAT pathway accompanying glial activation after LPS treatment, were followed by analyzing secreted proinflammatory cytokine levels. The administration of LPS caused tyrosine phosphorylation of STAT3 in retinae and induced glial fibrillary acidic protein. (GFAP) from the nerve fiber layer to the ganglion cell layer. Our results suggest that the LPS-induced activation of the JAK2/STAT3 signaling pathway may play a key role in the induction of astrogliosis. However, no significant increase in vimentin, OX-42 or inducible nitric oxide synthase (iNOS) expressions were observed after LPS administration. Sphingosine kinase catalyzes the conversion of sphingosine to sphingosine-1–phosphate (So-1-P), a sphingolipid metabolite that plays important roles in angiogenesis, inflammation, and cell growth. In the present study, it was found that sphingolipid metabolite levels were elevated in the serum and retinae of LPS-injected rats. To further investigate the chronic effect of increased So-1-P in the retina, So-1-P was infused intracerebroventricularly (i.c.v.) into rats using an osmotic minipump at 100 pmol/10 μl h^-1 for 7 days, and was found to increase retinal GFAP expression. These observations suggest that LPS induces the activation of retinal astrocytes via JAK2/STAT3 and that LPS affects So-1-P generation. Our findings also suggest that elevated So-1-P in the retina and/or in serum could induce cytochemical alterations in LPS treated or inflamed retinae.     

激光视网膜损伤治疗的实验研究

为研究碱性成纤维细胞生长因子（basic fibroblast growth factor,bFGF）,地塞松和维生素C对激光视网膜损伤的治疗作用,将采用氩离子激光照射致视网膜损伤的青紫蓝灰兔分9组（照射对照组、球后注射bFGF0.5、1.0、2.0μ.k.3D组和地塞米松1.0m.k.3D;肌肉注射bFGF1.0、2.0、4.0μ.k.D组和地塞米松2.0mg加维生素C200.0mg组）。恒河猴分4组（照射对照组、bFGF1.0、2.0μ.k.3D组和地塞米松1.0m.k.3D组）。通过视网膜电流图、检眼镜、眼底照相机、损伤斑面积测量、光镜和电镜观察,结果表明bFGF对视网膜损伤斑有明显的促进修复愈合作用。     

Malformation of Embryonic Neural Retina Elicited by BrdU

Exposure of neural retina tissue from early chick embryos (5 and 6-days) to 5-bromo-2'-deoxyuridine (BrdU) for 24 h irreversibly prevented normal histogenesis and resulted in the formation of chaotically disorganized tissue. The sensitivity of the retina to this effect decreased with embryonic age and declined sharply after the commencement of cell stratification. Examination by electron microscopy revealed the following progressive morphologic changes resulting from BrdU treatment: complete breakdown of the outer limiting membrane due to disappearance of its constituent tight junctions which normally anchor cells at the outer retinal surface; collapse and endocytosis of cilia, resulting in the absence of photoreceptor processes; increasing disorganization of the cells which commenced at the outer surface of the retina and progressed inward, resulting in chaotic distortion of the histologic architecture of the retina. Ultrastructural differences were noted between cells in the malformed retina, indicating the presence of several cell types. Possible mechanisms of this BrdU-elicited malformation are considered in the Discussion.     

Stimulus discrimination by horses under scotopic conditions

Scotopic vision in horses (Equus caballus) was investigated using behavioral measurements for the first time. Four horses were tested for the ability to make simple visual discriminations of geometric figures (circles and triangles) under various brightness levels within an enclosed building. Measurements of brightness ranging from 10.37 to 24.12 magnitudes per square arcsecond (mag/arcsec²; in candelas per square meter—7.70 to 2.43E-05 cd/m²) were taken using a Sky Quality Meter. These values approximated outdoor conditions ranging from twilight in open country to a dark moonless night in dense forest. The horses were able to solve the discrimination problems in all brightness settings up to 23.77 mag/arcsec² (3.35E-05 cd/m²). Moreover, they easily navigated their way around obstacles located within the testing area in extremely dim light (>23.50 mag/arcsec²; 4.30E-05 cd/m²), which were in conditions too dark for the human experimenters to see. These findings support physiological data that reveal a rod-dominated visual system as well as observations of equine activity at night.     

Local Differences in GABA Release Induced by Excitatory Amino Acids During Retina Development: Selective Activation of NMDA Receptors by Aspartate in the Inner Retina

Glutamate and GABA are the major excitatory and inhibitory neurotransmitters in the CNS. In the retina, it has been shown that glutamate and aspartate and their agonists kainate and NMDA promote the release of GABA. In the chick retina, at embryonic day 14 (E14), glutamate and kainate were able to induce the release of GABA from amacrine and horizontal cells as detected by GABA-immunoreactivity. NMDA also induced GABA release restricted to amacrine cell population and its projections to the inner plexiform layer (E14 and E18). Although aspartate reduced GABA immunoreactivity, specifically in amacrine cells of E18 retinas, it was not efficient to promote GABA release from retinas at E14. As observed in differentiated retinas, dopamine inhibited the GABA release promoted by NMDA and aspartate but not by kainate. Our data show that different retinal sites respond to distinct EAAs via different receptor systems.     

Uridine Metabolism in the Goldfish Retina During Optic Nerve Regeneration: Whole Retina Studies

Accumulation of radioactivity from [3H]uridine in incubations of whole goldfish retinas is increased in the ipsilateral retina during a period of regeneration that follows unilateral optic nerve crush. Brief incubations to investigate the nature of enhanced labeling of the acid-soluble fraction showed a peak uptake 4 days following crush, with a gradual decrease to control levels by 21 days following crush. That nucleoside uptake may not mediate the effect is supported by the observation that the rate of uptake of 5'-deoxyadenosine, a nonmetabolizable nucleoside analog, is the same in post-crush (PC) and normal (N) retinal incubations. Following brief incubations of PC and N retinas with [3H]uridine, there is enhanced labeling in PC retinas relative to N retinas of recovered UMP, UDP, UTP, and uridine nucleotide sugars, whereas recovery of labeled uridine itself is slightly decreased. The results suggest that the increased accumulation of radioactivity in PC retinas following incubation with uridine reflects an increase in the activities of retinal uridine kinase and uridine nucleotide kinases.     

Demonstration of Transdifferentiation of Neural Retina from Pigmented Retina in Culture1

The formation of neural retina (NR) from retinal pigmented epithelium (RPE) of chick embryos in culture was investigated. In cultures of explants of PRE, depigmented, preretinal foci, consisting of 50 to 100 cells appeared in the pigmented central portion of the explant within three days. Then these depigmented cells increased rapidly in number and by about day 14 they formed characteristic spherical bodies, which were identified as a neural retinal-like structure (NR structure) by electron microscopic observations. Culture of explants of RPE from embryos of different stages showed that the capacity of embryonic RPE to form an NR structure decreased steadily with embryonic age from st. 24 to 27. At and after stage 27, no foci leading to the neural retinal differentiation were formed in the explants. Medium conditioned by cell cultures of chicken embryonic NR, RPE or chondrocytes had no effect on the formation of NR structures by explants of RPE.     

Modulation by Docosahexaenoic Acid of the Epinephrine-Stimulated Adenylate Cyclase Activity of the Bovine Retina

This work shows that unsaturated fatty acids enhance the epinephrine-stimulated adenylate cyclase activity in bovine retina. The modulating effect on the epinephrine-stimulated formation of cyclic AMP seems to be linked to the degree of unsaturation of the fatty acid. Treatment of the intact retina with docosahexaenoic acid in the concentration range 0.5 X 10(-6)-1 X 10(-3) M does not affect the enzyme activity measured in the absence of the hormone but markedly increases the cyclase activity when the tissue is incubated in the presence of 0.1 mM epinephrine. Docosahexaenoic acid enhances the maximal response to epinephrine without affecting the apparent ED50 value for this effector. Docosahexaenoic acid at 0.5 mM also increases the hormone-stimulated adenylate cyclase activity in retinal cell-free homogenate, whereas it has no effect on the epinephrine-sensitive enzyme solubilized from the membrane fraction with 1% Triton X-305. When docosahexaenoic acid-preincubated intact retina and cell-free homogenate are incubated in the presence of defatted albumin, both the observed activating effect of the fatty acid on the epinephrine-stimulated adenylate cyclase activity and the enhancement of the enzyme response to the hormone significantly diminish.     

Dopaminergic Mechanisms in the Teleost Retina

A specific dopamine-sensitive adenylate cyclase has been identified in homogenates of the teleost (carp) retina. Maximal stimulation by 100 microM-dopamine resulted in a 5--10-fold increase in adenylate cyclase activity with half-maximal stimulation occurring at a concentration of 1 microM. l-Noradrenaline and l-adrenaline were some 10 times less potent than dopamine whilst the alpha- and beta-adrenoreceptor agonists, l-phenylephrine and dl-isoprenaline were inactive. Apomorphine elicited a partial stimulation of adenylate cyclase activity whilst various ergot alkaloids produced mixed agonist/antagonist responses. Dopamine-stimulated adenylate cyclase activity was potently antagonised by various neuroleptic drugs including fluphenazine, alpha-flupenthixol and alpha-piflutixol, and to a lesser extent by the butyrophenone derivatives haloperidol and spiperone. The benzamide derivatives, metoclopramide and sulpiride, together with the alpha- and beta-adrenoreceptor blocking agents, phentolamine and propranolol respectively were essentially inactive at blocking dopamine-stimulated adenylate cyclase activity. These data suggest the presence of a highly specific dopamine-sensitive adenylate cyclase in homogenates of teleost retina possessing similar pharmacological properties to the dopamine-sensitive adenylate cyclase observed in the mammalian central nervous system.     

Structure-Function Correlation of the Human Central Retina

Background

The impact of retinal pathology detected by high-resolution imaging on vision remains largely unexplored. Therefore, the aim of the study was to achieve high-resolution structure-function correlation of the human macula in vivo.

Methodology/Principal Findings

To obtain high-resolution tomographic and topographic images of the macula spectral-domain optical coherence tomography (SD-OCT) and confocal scanning laser ophthalmoscopy (cSLO), respectively, were used. Functional mapping of the macula was obtained by using fundus-controlled microperimetry. Custom software allowed for co-registration of the fundus mapped microperimetry coordinates with both SD-OCT and cSLO datasets. The method was applied in a cross-sectional observational study of retinal diseases and in a clinical trial investigating the effectiveness of intravitreal ranibizumab in macular telangietasia type 2. There was a significant relationship between outer retinal thickness and retinal sensitivity (p<0.001) and neurodegeneration leaving less than about 50 µm of parafoveal outer retinal thickness completely abolished light sensitivity. In contrast, functional preservation was found if neurodegeneration spared the photoreceptors, but caused quite extensive disruption of the inner retina. Longitudinal data revealed that small lesions affecting the photoreceptor layer typically precede functional detection but later cause severe loss of light sensitivity. Ranibizumab was shown to be ineffective to prevent such functional loss in macular telangietasia type 2.

Conclusions/Significance

Since there is a general need for efficient monitoring of the effectiveness of therapy in neurodegenerative diseases of the retina and since SD-OCT imaging is becoming more widely available, surrogate endpoints derived from such structure-function correlation may become highly relevant in future clinical trials.     

Optimal Stimulus Coding by Neural Populations Using Rate Codes

We create a framework based on Fisher information for determining the most effective population coding scheme for representing a continuous-valued stimulus attribute over its entire range. Using this scheme, we derive optimal single- and multi-neuron rate codes for homogeneous populations using several statistical models frequently used to describe neural data. We show that each neuron's discharge rate should increase quadratically with the stimulus and that statistically independent neural outputs provides optimal coding. Only cooperative populations can achieve this condition in an informationally effective way.     

Rubber Hand Illusion Reduces Discomfort Caused by Cold Stimulus

There is a growing interest in body-ownership disruptions and their consequences for subjective experiences such as tactile sensations or pain. Here, we investigated the effect of the rubber hand illusion (RHI) on the perceived discomfort caused by cold stimulus applied to the real hand. The results showed reduced discomfort to cold reflected in behavioural and subjective measures. The stronger the illusion, the later the cold temperature became unpleasant and the less intense the experience was rated. We discuss the link between thermoception and body ownership as well as possible theoretical and methodological implications for studies on pain experience under RHI.