The effect of oxygen and light on the structure and function of the neonatal rat retina

Effects of Dietary Sodium and Chloride on Slaughter Performance, Digestive Tract Development and Tibia Mineralization of Geese

This study evaluated the slaughter performance, digestive tract development and tibia mineralization effects of sodium (Na) and chloride (Cl) on geese. Four hundred and thirty-four male geese at 29 days were randomly assigned into nine groups with six replicates (eight in each). The experiment employed a 3 × 3 factorial design, with two instances each of three Na levels (0.10%, 0.15%, and 0.20%) and three Cl levels (0.15%, 0.20%, and 0.25%). All experimental birds were husbanded for 42 days. Dietary Na and Cl levels and their interactions (Na ×Cl) had no significant effect on the slaughter, breast, thigh, abdominal fat yield, and digestive tract index of geese (p > 0.05). However, dietary Na and Cl level significantly affected the crypt depth of the jejunum and tibial development. Variations in Na and Cl levels had a significant interaction on the crypt depth of jejunal (p < 0.05), 0.20% Na × 0.25% Cl had a minor crypt depth. Dietary variations in Na and Cl significantly affected the tibial strength, and there was a significant interaction between them (p < 0.05). When Na and Cl were at their maximum (0.20% Na and 0.25% Cl), the strength of the tibia was the lowest. In addition, a single factor (Na or Cl) had no effect (p > 0.05), but its interaction significantly affected the calcium (Ca) content of bone (p < 0.05). When the Na and Cl levels were 0.15% and 0.15%, respectively, the Ca content in bone was the highest. These results suggest that dietary Na and Cl had interactive effects on geese, especially in the development of the tibia. High dietary Na and Cl levels adversely influenced the tibia and intestinal crypt morphology. Therefore, we do not advocate supplementing too much Na or Cl in the diet. Combined with our previous results, for 29-70-day-old geese, it is recommended that dietary Na and Cl levels should be 0.10% and 0.15%, respectively.

Combination Antioxidant/NSAID Therapies and Oral/Topical Ocular Delivery Modes for Prevention of Oxygen-Induced Retinopathy in a Rat Model

Given the complexity of oxygen-induced retinopathy (OIR), we tested the hypothesis that combination therapies and modes of administration would synergistically optimize efficacy for prevention of OIR. Newborn rats were exposed to neonatal intermittent hypoxia (IH) from the first day of life (P0) until P14 during which they received: (1) oral glutathione nanoparticles (nGSH) with topical ocular phosphate buffered saline (PBS); (2) nGSH with topical ocular Acuvail (ACV); (3) oral coenzyme Q10 (CoQ10) + ACV; (4) oral omega 3 polyunsaturated fatty acids (n-3 PUFAs) + ACV; (5) CoQ10 + n-3 PUFAs + PBS; or (6) CoQ10 + n-3 PUFAs + ACV. Treated groups raised in room air (RA) served as controls. At P14, pups were placed in RA with no treatment until P21. Retinal vascular pathology, ocular angiogenesis biomarkers, histopathology, and morphometry were determined. All combination treatments in IH resulted in the most beneficial retinal outcomes consistent with suppression of angiogenesis growth factors during reoxygenation/reperfusion and no significant adverse effects on somatic growth. nGSH + PBS also reversed IH-induced retinopathy, but had negative effects on growth. Simultaneously targeting oxidants, inflammation, and poor growth mitigates the damaging effects of neonatal IH on the developing retina. Therapeutic synergy with combination delivery methods enhance individual attributes and simultaneously target multiple pathways involved in complex diseases such as OIR.

Bumetanide Suppression of Angiogenesis in a Rat Model of Oxygen-Induced Retinopathy

Aquaporins (AQPs) are involved in hypoxia-induced angiogenesis and retinal damage. Bumetanide is a diuretic agent, Na⁺/K⁺/Cl⁻ cotransporter (NKCC1), and AQP 1–4 inhibitor. We tested the hypothesis that early postnatal treatment with bumetanide suppresses biomarkers of angiogenesis and decreases severe retinopathy oxygen-induced retinopathy (OIR). Neonatal rats were exposed at birth (P0) to either (1) room air (RA); (2) hyperoxia (50% O₂); or (3) intermittent hypoxia (IH) consisting of 50% O₂ with brief, clustered episodes of 12% O₂ from P0 to postnatal day 14 (P14), during which they were treated intraperitoneally (IP) with bumetanide (0.1 mg/kg/day) or an equivalent volume of saline, on P0–P2. Pups were examined at P14 or allowed to recover in RA from P14–P21. Retinal angiogenesis, morphometry, pathology, AQPs, and angiogenesis biomarkers were determined at P14 and P21. Bumetanide reduced vascular abnormalities associated with severe OIR. This was associated with reductions in AQP-4 and VEGF. Bumetanide suppressed sVEGFR-1 in the serum and vitreous fluid, but levels were increased in the ocular tissues during recovery. Similar responses were noted for IGF-I. In this model, early systemic bumetanide administration reduces severe OIR, the benefits of which appear to be mediated via suppression of AQP-4 and VEGF. Further studies are needed to determine whether bumetanide at the right doses may be considered a potential pharmacologic agent to treat retinal neovascularization.

Thioredoxin 1 Plays a Protective Role in Retinas Exposed to Perinatal Hypoxia-Ischemia

Thioredoxin family proteins are key modulators of cellular redox regulation and have been linked to several physiological functions, including the cellular response to hypoxia-ischemia. During perinatal hypoxia-ischemia (PHI), the central nervous system is subjected to a fast decrease in O₂ and nutrients with a subsequent reoxygenation that ultimately leads to the production of reactive species impairing physiological redox signaling. Particularly, the retina is one of the most affected tissues, due to its high oxygen consumption and exposure to light. One of the main consequences of PHI is retinopathy of prematurity, comprising changes in retinal neural and vascular development, with further compensatory mechanisms that can ultimately lead to retinal detachment and blindness. In this study, we have analyzed long-term changes that occur in the retina using two well established in vivo rat PHI models (perinatal asphyxia and carotid ligation model), as well as the ARPE-19 cell line that was exposed to hypoxia and reoxygenation. We observed significant changes in the protein levels of the cytosolic oxidoreductase thioredoxin 1 (Trx1) in both animal models and a cell model. Knock-down of Trx1 in ARPE-19 cells affected cell morphology, proliferation and the levels of specific differentiation markers. Administration of recombinant Trx1 decreased astrogliosis and improved delayed neurodevelopment in animals exposed to PHI. Taken together, our results suggest therapeutical implications for Trx1 in retinal damage induced by hypoxia-ischemia during birth.

Evaluating the neuroprotective effect of 17β-estradiol in rodent models of oxidative retinopathies

PURPOSE

To determine the neuroprotective effect of estrogen on the structure and function of the retina exposed to an oxidative stress.

METHODS

Male Sprague-Dawley rat pups were exposed to either hyperoxia (O₂E: from P8 to P14) or bright light (LE: from P14 to P28) with or without 17 β-estradiol (βE₂) treatment. Retinal structure (histology) and function (ERG) were assessed at selected time points.

RESULTS

In the O₂E model, βE₂ injections caused a significant reduction of the ERG and a significantly thinner OPL compared to untreated oxygen-exposed group (O₂-exposed) rats. In contrast, in the LE model βE₂, treatment was beneficial to the retinal structure (thicker ONL) and function (better preserved ERG amplitudes) compared to untreated light-exposed group (light-exposed rats).

CONCLUSION

Our results show that in conditions where the primary target of the oxidative stress is the outer retina (i.e., the photoreceptors) estrogen can protect the retina, while in situations where the inner retina (or retinal vasculature) is the main site of oxidative damage, estrogen may potentiate the detrimental effect of oxidative stress on the retina.

Eye and Associated Glands

The eye is susceptible to adverse toxic effects by direct application, inadvertent ocular contact, or systemic exposure to chemicals or their metabolites. Although the albino rat is a less than ideal model for ocular toxicity studies, it has gained popularity for specific applications and may be the first species in which the ocular toxicity of a systemically administered xenobiotic becomes evident. This chapter reviews the embryology, anatomy, and physiology of the eye and associated glands and describes common nonneoplastic and neoplastic lesions encountered in laboratory rats.

Revisiting the mouse model of oxygen-induced retinopathy

Abnormal blood vessel growth in the retina is a hallmark of many retinal diseases, such as retinopathy of prematurity (ROP), proliferative diabetic retinopathy, and the wet form of age-related macular degeneration. In particular, ROP has been an important health concern for physicians since the advent of routine supplemental oxygen therapy for premature neonates more than 70 years ago. Since then, researchers have explored several animal models to better understand ROP and retinal vascular development. Of these models, the mouse model of oxygen-induced retinopathy (OIR) has become the most widely used, and has played a pivotal role in our understanding of retinal angiogenesis and ocular immunology, as well as in the development of groundbreaking therapeutics such as anti-vascular endothelial growth factor injections for wet age-related macular degeneration. Numerous refinements to the model have been made since its inception in the 1950s, and technological advancements have expanded the use of the model across multiple scientific fields. In this review, we explore the historical developments that have led to the mouse OIR model utilized today, essential concepts of OIR, limitations of the model, and a representative selection of key findings from OIR, with particular emphasis on current research progress.

A histological and immunohistochemical study of the effects of N-acetyl cysteine on retinopathy of prematurity by modifying insulin-like growth factor-1

Retinopathy of prematurity (ROP) is a vasoproliferative disorder that occurs in premature infants and may lead to permanent visual impairment. We investigated both the possible protective role of N-acetyl cysteine (NAC) for preventing ROP and the role of IGF-1 in the disorder. Forty-five newborn rats were divided into three groups. Group 1 was raised in room air as controls. Group 2 was exposed to 60% oxygen for 14 days after birth, then transferred to room air. Group 3 was exposed to the same conditions as group 2, but received intraperitoneal injections of NAC on postnatal days 7-17. After 35 days, both eyes of all rats were processed for histology. Some sections were stained with hematoxylin and eosin to assess structural changes and other sections were immunostained to determine the location of IGF-1. Frozen sections also were prepared and stained for adenosine triphosphatase to detect retinal blood vessels. Compared to the controls, more blood vessels, many of which were abnormal, and increased IGF-1 expression were observed in group 2. In group 3, abnormal blood vessels and IGF-1 expression were less evident. NAC appeared to be an effective vascular-protective agent for ROP by decreasing IGF-1 expression.

Toll-like receptor 3 activation drives the inflammatory response in oxygen-induced retinopathy in rats

AIMS

Ischaemia is one of the most important causes of blindness. The purpose of this study was to investigate the potential role and mechanisms by which toll-like receptor 3 (TLR3) influences the progression of the inflammatory response in a rat model of oxygen-induced retinopathy (OIR).

METHODS

OIR rat models were successfully established and received single intravitreal injections of polyinosine-polycytidylic acid (poly (I:C)) and anti-TLR3 antibody, respectively, on postnatal day 17 (P17). Pathological retinal neovascularisation was evaluated by haematoxylin and eosin staining and immunohistochemistry with Isolectin B4 FITC (fluorescein isothyocyanate). Retinal expressions of TLR3 and nuclear factor kappa B (NF-κB) were measured using real-time PCR, immunohistochemistry and western blot. Furthermore, interleukin-6 (IL-6) and tumour necrosis factor α (TNFα) expression levels were assessed with real-time PCR and ELISA.

RESULTS

Both gene and protein expression levels of TLR3 and NF-κB were significantly elevated in the retinas of OIR rats compared to the controls. Increased IL-6 and TNFα expression levels were also observed in the retinas of OIR rats. Furthermore, TLR3 signalling pathway components, including NF-κB and IL-6/TNFα, were markedly upregulated upon stimulation with poly(I:C). In addition, the pre-treatment of TLR3 neutralising antibody in OIR models significantly decreased TLR3 and NF-κB expressions, as well as related inflammatory factors IL-6/TNFα expression.

CONCLUSIONS

Our results suggest that upregulation of the TLR3 signalling pathway is involved in the pro-inflammatory response in OIR rat retinas.

Assessment of vascular regeneration in the CNS using the mouse retina

The rodent retina is perhaps the most accessible mammalian system in which to investigate neurovascular interplay within the central nervous system (CNS). It is increasingly being recognized that several neurodegenerative diseases such as Alzheimer's, multiple sclerosis, and amyotrophic lateral sclerosis present elements of vascular compromise. In addition, the most prominent causes of blindness in pediatric and working age populations (retinopathy of prematurity and diabetic retinopathy, respectively) are characterized by vascular degeneration and failure of physiological vascular regrowth. The aim of this technical paper is to provide a detailed protocol to study CNS vascular regeneration in the retina. The method can be employed to elucidate molecular mechanisms that lead to failure of vascular growth after ischemic injury. In addition, potential therapeutic modalities to accelerate and restore healthy vascular plexuses can be explored. Findings obtained using the described approach may provide therapeutic avenues for ischemic retinopathies such as that of diabetes or prematurity and possibly benefit other vascular disorders of the CNS.

Oxygen-induced retinopathy induces short-term glial stress and long-term impairment of photoentrainment in mice

BACKGROUND

Retinopathy of prematurity is a serious potentially blinding disease of pre-term infants. There is extensive vascular remodeling and tissue stress, but data concerning alterations in retinal neurons and glia, and long-term functional sequelae are still incomplete.

METHODS

ROP was induced using the oxygen-induced retinopathy (OIR) mouse model. Postnatal day 7 (P7) 129SVE mice were exposed to hyperoxia (75 ± 0.5 % oxygen) for 5 days, and then returned to normoxia to induce OIR. Exposed animals were euthanized at 5 (P17-OIR) and 14 days (P26-OIR) after return to normal air, together with corresponding age-matched control mice (P17-C and P26-C respectively) raised only in room air. Their retinas were examined by immunohistochemistry using a battery of antibodies against key glial and neuronal proteins. A further group of OIR mice and controls were examined at 10 weeks of age for their ability to re-entrain to changing 12 h light/12 h dark cycles, assayed by wheel-running actimetry. In this protocol, animals were subjected to three successive conditions of 300 lux, 15 lux and 1 lux ambient light intensity coupled with 6 hours of jetlag. Animals were euthanized at 4 months of age and used in immunoblotting for rhodopsin.

RESULTS

Compared to P17-C, immunohistochemical staining of P17-OIR sections showed up-regulation of stress-related and glutamate-regulatory proteins in astrocytes and Müller glial cells. In contrast, glial phenotypic expression in P26-OIR retinas largely resembled that in P26-C. There was no loss in total retinal ganglion cells (RGC) at either P17-OIR or P26-OIR compared to corresponding controls, whereas intrinsically photosensitive RGC showed significant decreases, with 375 ± 13/field in P26-OIR compared to 443 ± 30/field in P26-C (p < 0.05). Wheel actimetry performed on control and OIR-treated mice at 4 months demonstrated that animals raised in hyperoxic conditions had impaired photoentrainment at low illuminance of 1 lux, as well as significantly reduced levels of rhodopsin compared to age-matched controls.

CONCLUSIONS

OIR leads to transient up-regulation of retinal glial proteins involved in metabolism, and partial degeneration of intrinsically photosensitive RGC and rod photoreceptors. OIR affects circadian photo-entrainment at low illuminance values, possibly by affecting the rod pathway and/or intrinsically photosensitive RGC input to the circadian clock. This study hence shows that retinopathy of prematurity affects light-regulated circadian behavior in an animal model, and may induce similar problems in humans.

Oxidative stress retards vascular development before neural degeneration occurs in retinal degeneration rd1 mice

PURPOSE

To investigate the role of reactive oxygen species (ROS) in retinal development during the early postnatal stage of rd1 mice.

METHODS

Development of the three retinal vascular layers of C57BL/6 J (WT) and C3H/HeN (rd1) mice was evaluated from 9th postnatal day (P9) to P21. Retinal ROS production was semi-quantitatively measured using dihydroethidium fluorescence. Mice were treated with intraperitoneal injections of 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPOL) at a dose of 275 mg/kg body weight, and PBS as the control from P3 to P8.

RESULTS

Rd1 mice showed retardation of retinal vascular development in the deep layer at P9. No significant difference was observed in the outer nuclear layer thickness of rd1 and WT mice. ROS production in the outer nuclear layer of rd1 mice was significantly higher than that in the outer nuclear layer of WT mice at P9, P13, and P17 (P < .05). TEMPOL facilitated the development of the deep vascular layer when compared with injection of PBS.

CONCLUSIONS

Retardation of retinal vascular development is observed in rd1 mice; ROS is partially responsible for this finding. When using rd1 mice, we should be aware of this difference in comparison to other retinal degeneration animal models and human pathophysiological changes.

Hydrogen peroxide accumulation in the choroid during intermittent hypoxia increases risk of severe oxygen-induced retinopathy in neonatal rats

PURPOSE

Extremely low gestational age neonates (ELGANs) requiring oxygen therapy often experience frequent episodes of intermittent hypoxia (IH) and are at high risk for severe retinopathy of prematurity (ROP). Using an established model for oxygen-induced retinopathy (OIR), we examined the hypothesis that there is a critical number of daily brief IH episodes which will result in irreversible retinal oxidative damage.

METHODS

Newborn rats were exposed to increasing daily clustered IH episodes (12% O₂ with 50% O₂) from postnatal day (P) 0 to P7 or P0 to P14, or placed in room air (RA) until P21 following 7- or 14-day IH. RA littermates at P7, P14, and P21 served as controls. A group exposed to constant 50% O₂ (CH) served as a second control. Blood gases, eye opening at P14, retinal, and choroidal oxidative stress and lipid peroxidation (8-isoPGF(2α)), oxidants (H₂O₂) and antioxidants (catalase and SOD), retinal pathology (adenosine diphosphatase (ADPase)-stained retinal flatmounts), and mitochondria-related genes were assessed.

RESULTS

pO₂ levels were higher with increasing IH episodes and remained elevated during the reoxygenation period. High SO₂ levels were associated with most severe OIR. Levels of all measured biomarkers peaked with six IH episodes and decreased with 8 to 12 episodes. H₂O₂ accumulated in the choroid during the reoxygenation period with irreversible retinal damage.

CONCLUSIONS

Our data suggest that six is the maximum number of IH episodes that the retina can sustain. Accumulation of H₂O₂ in the choroid may result in high levels being delivered to the entire retina, ultimately resulting in irreversible retinal oxidative damage.

Clinical and Rehabilitative Management of Retinitis Pigmentosa: Up-to-Date

The term retinitis pigmentosa (RP) indicates a heterogeneous group of genetic rare ocular diseases in which either rods or cones are prevalently damaged. RP represents the most common hereditary cause of blindness in people from 20 to 60 years old. In general, the different RP forms consist of progressive photo-receptorial neuro-degenerations, which are characterized by variable visual disabilities and considerable socio-sanitary burden. Sometimes, RP patients do not become visually impaired or legally blind until their 40-50 years of age and/or maintain a quite acceptable sight for all their life. Other individuals with RP become completely blind very early or in middle childhood. Although there is no treatment that can effectively cure RP, in some case-series the disease's progression seems to be reducible by specific preventive approaches. In the most part of RP patients, the quality of vision can be considerably increased by means of nanometer-controlled filters. In the present review, the main aspects of the routine clinical and rehabilitative managements for RP patients are described, particularly focusing on the importance of specific referral Centers to practice a real multidisciplinary governance of these dramatic diseases.

Paradoxical effects of alcohol and thiamine deficiency on the eye opening in rat pups

OBJECTIVE

The present study attempts to determine whether developmental thiamine (B1 vitamin) deficiency and developmental ethanol exposure disturb eye opening in Wistar rat pups.

METHODS

During gestation and lactation, Wistar rat dams were exposed to the following treatments: (1) Prenatal thiamine-deficient dams; (2) perinatal thiamine-deficient dams; (3) postnatal thiamine-deficient dams; (4) 12% alcohol/water drinking mothers; (5) mothers drinking 12% alcohol/water + thiamine hydrochloride mixture; (6) ad libitum control dams. Pair-feeding treatments controlled malnutrition related to thiamine deficiency: (7) Prenatal pair-fed dams; (8) perinatal pair-fed dams; (9) postnatal pair-fed dams and included also the control of alcohol consummation: (10) pair-fed saccharose dams. After birth, from postnatal day 10 (P10) to P18, eye opening was observed in the pups bred by ten different experimental dams.

RESULTS

The present experiments showed eye opening to be delayed strongly in perinatal thiamine-deficient pups only. Consequently, our study suggests perinatal thiamine deficiency to interfere with photoreceptors differentiation in the rat retina. In addition, our results reveal that developmental alcohol exposure-induced premature eye opening contrasted paradoxically with perinatal thiamine deficiency-induced delayed opening.

CONCLUSIONS

The results suggest differential actions of alcohol and thiamine deficiency on cellular genesis in the rat retina.

Eyeing central neurons in vascular growth and reparative angiogenesis

The generation of blood vessels is a highly synchronized process requiring the coordinated efforts of several vascular and nonvascular cell populations as well as a stringent orchestration by the tissue being vascularized. Stereotyped angiogenesis is vital for both developmental growth and to restore tissue metabolic supply after ischemic events. Central neurons such as those found in the brain, spinal cord, and retina are vast consumers of oxygen and nutrients and therefore require high rates of perfusion by functional vascular networks to ensure proper sensory transmission. During a metabolic mismatch, such as that occurring during a cerebrovascular infarct or in ischemic retinopathies, there is increasing evidence that central neurons have an inherent ability to influence the vascular response to injury. With a focus on the retina and retinal ischemic disorders, this review explores the ever-growing evidence suggesting that central neurons have the propensity to impact tissue vascularization and reparative angiogenesis. Moreover, it addresses the paradoxical ability of severely ischemic neurons to hinder vascular regrowth and thus segregate the most severely injured zones of nervous tissue. The topics covered here are pertinent for future therapeutic strategies because promoting and steering vascular growth may be beneficial for ischemic disorders.

Protein adsorption and peroxidation of rat retinas under stimulation of a neural probe coated with polyaniline

For the purpose of investigating the potential use of conducting polymers, i.e. polyaniline (PANi), as electrode coating material for improving the function of neural probes, a PANi-coated platinum (Pt) electrode was prepared by the in situ polymerization method. Protein adsorption was observed by atomic force microscopy/scanning electron microscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis, as well as quantification. Peroxidation of rat retinas was evaluated by determination of conjugated dienes and PLOOH, which were quantified by UV-visible spectrophotometer and high-performance liquid chromatography. The stability of PANi coating for 6 months was also estimated with an in vitro electrical stimulation system. This revealed that: (1) PANi with regular and compact nanoparticles 20-40 nm in diameter was successfully polymerized on the uncoated platinum electrode surface; (2) the PANi-coated Pt electrode adsorbed fewer retinal fragments and induced less peroxidation than the uncoated platinum electrode; (3) in contrast to the uncoated platinum electrode, the PANi-coated Pt electrode surface tended to aggregate retinal fragments rather than spread them, which may help to reduce inflammation and scar formation in long-term implantation; (4) the PANi coating exhibited excellent properties in terms of the intactness and the stable nanoparticle morphology after 6 months' electrical stimulation, while corrosion occurred on the uncoated platinum electrode after 1 month.

Role of Nrf2 in retinal vascular development and the vaso-obliterative phase of oxygen-induced retinopathy

In the initial stage of retinopathy of prematurity (ROP), hyperoxia causes retinal blood vessel obliteration. This is thought to occur in part through oxidative stress-induced apoptosis of endothelial cells. This study was designed to determine what role NF-E2-related factor 2 (Nrf2) plays in this process. Nrf2 is a transcription factor of the anti-oxidant response element that, if induced, may protect the retina from hyperoxia-induced oxidative stress. Nrf2 knockout mice (Nrf2-/-), Nrf2 wild type control mice (Nrf2+/+), and C57BL/6 mice were exposed to hyperoxia (75% O(2)) or normoxia from P7 through P12. Mice were sacrificed on P9 and P12 and the retinas were stained with GSA lectin-Cy3 to visualize retinal blood vessels. Hyperoxia exposed retinas were flat mounted and photographed, then the size of the avascular areas was determined. Additionally, retinas were cryopreserved after lectin staining and area analysis and then sectioned. Secondary or deep capillaries were then hand-counted in sections. In hyperoxia-treated mice, the avascular areas in Nrf2-/- P9 mice were significantly larger than those in Nrf2+/+ P9 mice (P = 0.01). However, there was no significant difference between Nrf2-/- and Nrf2+/+ mice at P12. Avascular areas at P12 were significantly smaller than that at P9 in Nrf2-/-, Nrf2+/+, and C57BL/6 mice (P = 0.0011, P = 0.009, and P = 0.001 respectively). The numbers of deep or secondary capillaries in air-reared Nrf2-/- mice were significantly decreased, when compared to Nrf2+/+ mice at P9 (P = 0.0082). On the other hand, there was no significant difference in deep capillary formation between air-reared Nrf2-/- and Nrf2+/+ mice at P12. Akt signaling activates Nrf2 and Akt was localized to retinal blood vessels in all animals and was increased in Nrf2+/+ and Nrf2-/- mice exposed to hyperoxia as compared to normoxia mice. Interestingly, during normal development this protection by Nrf2 occurs in a specific window of time that is also shared by angiogenesis. Hyperoxia treatment revealed a similar window of time where Nrf2 regulated anti-oxidant production was beneficial and contributed to the endothelial survival.

Oxygen supply and consumption in the retina: implications for studies of retinopathy of prematurity

A disrupted oxygen environment in the retina of severely premature neonates is thought to be a key factor in the development of retinopathy of prematurity (ROP). This review describes our understanding of intraretinal oxygen distribution and consumption in a range of animal models, including species with naturally avascular retinas and models of induced occlusion of the retinal vasculature. The influence of graded systemic hyperoxia on retinal oxygenation is also discussed along with modulation of retinal oxygen metabolism. The differences in retinal oxygenation between developing and mature retinas are also described. Comparisons are made with studies in the monkey retina in order to assess possible similarities in behaviour between rat and human retinas. Pathogenesis mechanism and possible intervention strategies during the diseased processes in ROP are proposed based on our current knowledge.

The anatomy of the rat eye with oxygen-induced retinopathy

Prior studies have documented the intertwined developmental courses of retinal blood vessel tortuosity (in fundus photographs) and retinal dysfunction (in electroretinographs) in Sprague-Dawley rat models of retinopathy of prematurity (ROP). Two such models, the "50/10 model" and the "75 model," are named after the oxygen regimens used to induce retinopathy and are characterized by distinct neurovascular courses that span a range of disease severity. In this study of 50/10 and 75 model rats, retinal flatmounts were used to study the full vasculature at postnatal day (P) 15, P19 and P30. In addition, the layers of the neural retina were measured in toluidine blue-stained cross sections. Finally, gross anatomic features of the eye, including axial length, retinal surface area, and the ratio of anterior to posterior axial-lengths were evaluated. Both clock hours of neovascularization (NV) and percent avascular retina (AR) peaked at P19 and resolved by P30. Through P19, NV was found in every 50/10 model rat, but in only 60% of 75 model rats. AR was positively related to NV. All inner layers of the retina (outer plexiform layer through ganglion cell layer) were attenuated in 50/10 model rats but, in the 75 model, no layer differed significantly from that in controls. The eyes in both ROP models were smaller than those of age-matched controls. The ratio of anterior to posterior axial-lengths ranged from 0.45 in controls through 0.37 in the 75 model to 0.32 in the 50/10 model. Thus, eye growth is altered in these rat models of ROP.