Enriched environment and visual stimuli protect the retinal pigment epithelium and photoreceptors in a mouse model of non-exudative age-related macular degeneration.

Non-exudative age-related macular degeneration (NE-AMD), the main cause of blindness in people above 50 years old, lacks effective treatments at the moment. We have developed a new NE-AMD model through unilateral superior cervical ganglionectomy (SCGx), which elicits the disease main features in C57Bl/6J mice. The involvement of oxidative stress in the damage induced by NE-AMD to the retinal pigment epithelium (RPE) and outer retina has been strongly supported by evidence. We analysed the effect of enriched environment (EE) and visual stimulation (VS) in the RPE/outer retina damage within experimental NE-AMD. Exposure to EE starting 48 h post-SCGx, which had no effect on the choriocapillaris ubiquitous thickness increase, protected visual functions, prevented the thickness increase of the Bruch's membrane, and the loss of the melanin of the RPE, number of melanosomes, and retinoid isomerohydrolase (RPE65) immunoreactivity, as well as the ultrastructural damage of the RPE and photoreceptors, exclusively circumscribed to the central temporal (but not nasal) region, induced by experimental NE-AMD. EE also prevented the increase in outer retina/RPE oxidative stress markers and decrease in mitochondrial mass at 6 weeks post-SCGx. Moreover, EE increased RPE and retinal brain-derived neurotrophic factor (BDNF) levels, particularly in Müller cells. When EE exposure was delayed (dEE), starting at 4 weeks post-SCGx, it restored visual functions, reversed the RPE melanin content and RPE65-immunoreactivity decrease. Exposing animals to VS protected visual functions and prevented the decrease in RPE melanin content and RPE65 immunoreactivity. These findings suggest that EE housing and VS could become an NE-AMD promising therapeutic strategy.

Melatonin protects the retina from experimental nonexudative age-related macular degeneration in mice.

Nonexudative age-related macular degeneration (NE-AMD) represents the leading cause of blindness in the elderly. Currently, there are no available treatments for NE-AMD. We have developed a NE-AMD model induced by superior cervical ganglionectomy (SCGx) in C57BL/6J mice, which reproduces the disease hallmarks. Several lines of evidence strongly support the involvement of oxidative stress in NE-AMD-induced retinal pigment epithelium (RPE) and outer retina damage. Melatonin is a proven and safe antioxidant. Our aim was analysing the effect of melatonin in the RPE/outer retina damage within experimental NE-AMD. The treatment with melatonin starting 48 h after SCGx, which had no effect on the ubiquitous choriocapillaris widening, protected visual functions and avoided Bruch´s membrane thickening, RPE melanin content, melanosome number loss, retinoid isomerohydrolase (RPE65)-immunoreactivity decrease, and RPE and hotoreceptor ultrastructural damage induced within experimental NE-AMD exclusively located at the central temporal (but not nasal) region. Melatonin also prevented the increase in outer retina/RPE oxidative stress markers and a decrease in mitochondrial mass at 6 weeks post-SCGx. Moreover, when the treatment with melatonin started at 4 weeks post-SCGx, it restored visual functions and reversed the decrease in RPE melanin content and RPE65-immunoreactivity. These findings suggest that melatonin could become a promising safe therapeutic strategy for NE-AMD.

Enriched environment provides neuroprotection against experimental glaucoma.

Glaucoma is one of the most frequent causes of visual impairment worldwide, and involves selective damage to retinal ganglion cells (RGCs) and their axons. We analyzed the effect of enriched environment (EE) housing on the optic nerve, and retinal alterations in an induced model of ocular hypertension. For this purpose, male Wistar rats were weekly injected with vehicle or chondroitin sulfate (CS) into the eye anterior chamber for 10 weeks and housed in standard environment or EE. EE housing prevented the effect of experimental glaucoma on visual evoked potentials, retinal anterograde transport, phosphorylated neurofilament-immunoreactivity, axon number, microglial/macrophage reactivity (ionized calcium binding adaptor molecule 1-immunoreactivity), and astrocytosis (glial fibrillary acidic protein-immunostaining), as well as oligodendrocytes alterations (luxol fast blue staining, and myelin basic protein-immunoreactivity) in the proximal portion of the optic nerve. Moreover EE prevented the increase in ionized calcium binding adaptor molecule-1 levels, and RGC loss (Brn3a-immunoreactivity) in the retina from hypertensive eyes. EE increased retinal brain-derived neurotrophic factor levels. When EE housing started after 6 weeks of ocular hypertension, a preservation of visual evoked potentials amplitude, axon, and Brn3a(+) RGC number was observed. Taken together, these results suggest that EE preserved visual functions, reduced optic nerve axoglial alterations, and protected RGCs against glaucomatous damage.

Critical Role of Monocyte Recruitment in Optic Nerve Damage Induced by Experimental Optic Neuritis.

Neuroinflammatory diseases are characterized by blood-brain barrier disruption (BBB) and leukocyte infiltration. We investigated the involvement of monocyte recruitment in visual pathway damage provoked by primary optic neuritis (ON) induced by a microinjection of bacterial lipopolysaccharide (LPS) into the optic nerve from male Wistar rats. Increased Evans blue extravasation and cellularity were observed at 6 h post-LPS injection. In WT-GFPþ/WT chimeric rat optic nerves, the presence of GFP(+) neutrophils and GFP(+) monocytes, and in wild-type rat optic nerves, an increase in CD11b+CD45low and CD11b+CD45high cell number, were observed at 24 h post-LPS. Gamma-irradiation did not affect the increase in BBB permeability, but significantly lessened the decrease in pupil light reflex (PLR), and retinal ganglion cell (RGC) number induced by LPS. At 6 h post-LPS, an increase in chemokine (C-C motif) ligand 2 (CCL2) immunoreactivity co-localized with neutrophils (but not microglia/macrophages or astrocytes) was observed, while at 24 h post-injection, an increase in Iba-1-immunoreactivity and its co-localization with CCL2 became evident. The co-injection of LPS with bindarit (a CCL2 synthesis inhibitor) lessened the effect of LPS on PLR, and RGC loss. The treatment with etoposide or gadolinium chloride that significantly decreased peripheral monocyte (but not neutrophil or lymphocyte) percentage decreased the effect of LPS on PLR, and RGC number. Moreover, a negative correlation between PRL and monocyte (but not lymphocyte or neutrophil) percentage was observed at 7 days post-LPS. Taken together, these results support that monocytes are key players in the initial events that take place during primary ON.

Therapeutic benefit of environmental enrichment on optic neuritis.

Optic neuritis (ON) is an inflammatory, demyelinating, neurodegenerative, and presently untreatable condition of the optic nerve which might induce blindness. We analyzed the effect of environmental enrichment (EE) on visual pathway damage provoked by experimental ON induced by a microinjection of bacterial lipopolysaccharide (LPS) into the optic nerve. For this purpose, LPS was microinjected into the optic nerve from male Wistar rats. After injection, one group of animals was submitted to EE, and another group remained in standard environment (SE) for 21 days. EE prevented the decrease in pupil light reflex (PLR), visual evoked potentials, retinal anterograde transport, phosphorylated neurofilament immunoreactivity, myelination (luxol fast blue staining), and axon (toluidine blue staining) and retinal ganglion cell (Brn3a-immunoreactivity) number. EE also prevented microglial/macrophage reactivity (Iba-1- and ED1-immunoreactivity), and astrocytosis (glial fibrillary acidic protein-immunostaining) induced by experimental ON. LPS-injected optic nerves displayed oxidative damage and increased inducible nitric oxide synthase, cyclooxygenase-2, and interleukin-1ß and TNFα mRNA levels which were prevented by EE. EE increased optic nerve brain-derived neurotrophic factor levels. When EE started at 4 (but not 7) days post-injection of LPS, a preservation of the PLR was observed at 21 days post-LPS, which was blocked by the daily administration of ANA-12 from day 4 to day 7 post-LPS. Moreover, EE from day 4 to day 7 post-LPS significantly preserved the PLR at 21 days post-injection. Taken together, our data suggest that EE preserved visual functions and reduced neuroinflammation of the optic nerve. This article is part of the Special Issue entitled "Neurobiology of Environmental Enrichment".

Pre-ischemic enriched environment increases retinal resilience to acute ischemic damage in adult rats.

Retinal ischemia is a condition associated with several degenerative diseases leading to visual impairment and blindness worldwide. Currently, there is no highly effective therapy for ischemic retinopathies. This study was designed to determine possible benefits of pre-exposure to enriched environment against retinal damage induced by acute ischemia. For this purpose, adult male Wistar rats were randomly assigned to a pre-ischemic standard environment or a pre-ischemic enriched environment for 3 weeks, followed by unilateral ischemia induced by increasing intraocular pressure above 120 mm Hg for 40 min and reperfusion for 1 or 2 weeks in standard environment. Animals were subjected to electroretinography and histological analysis. Pre-ischemic enriched environment afforded significant functional protection in eyes exposed to ischemia/reperfusion injury. A marked reduction in retinal layer thickness, reduced synaptophysin-immunoreactivity and retinal ganglion cell (RGC) number, and increased microglia/macrophage reactivity were observed in ischemic retinas from animals submitted to pre-ischemic standard environment, which were prevented by pre-ischemic enriched environment. A deficit in anterograde transport from the retina to the superior colliculus and the lateral geniculate nucleus was observed in animals exposed to pre-ischemic standard environment, which was lower in animals previously exposed to enriched environment. The exposure to enriched environment before ischemia increased retinal brain derived neurotrophic factor (BDNF) protein levels in ischemic retinas and the administration of ANA-12 (a TrkB antagonist) abolished the protective effect of enriched environment on retinal function and retinal ganglion cell number. These results indicate that pre-ischemic enriched environment increases retinal resilience to acute ischemic damage, possibly through a BDNF/TrkB mediated pathway.

Neuroprotective effect of melatonin in experimental optic neuritis in rats.

Optic neuritis (ON) is an inflammatory, demyelinating, and neurodegenerative condition of the optic nerve, which might induce permanent vision loss. Currently, there are no effective therapies for this disorder. We have developed an experimental model of primary ON in rats through a single microinjection of 4.5 µg of bacterial lipopolysaccharide (LPS) into the optic nerve. Since melatonin acts as a pleiotropic therapeutic agent in various neurodegenerative diseases, we analyzed the effect of melatonin on LPS-induced ON. For this purpose, LPS or vehicle were injected into the optic nerve from adult male Wistar rats. One group of animals received a subcutaneous pellet of 20 mg melatonin at 24 hr before vehicle or LPS injection, and another group was submitted to a sham procedure. Melatonin completely prevented the decrease in visual evoked potentials (VEPs), and pupil light reflex (PLR), and preserved anterograde transport of cholera toxin ß-subunit from the retina to the superior colliculus. Moreover, melatonin prevented microglial reactivity (ED1-immunoreactivity, P < 0.01), astrocytosis (glial fibrillary acid protein-immunostaining, P < 0.05), demyelination (luxol fast blue staining, P < 0.01), and axon (toluidine blue staining, P < 0.01) and retinal ganglion cell (Brn3a-immunoreactivity, P < 0.01) loss, induced by LPS. Melatonin completely prevented the increase in nitric oxide synthase 2, cyclooxygenase-2 levels (Western blot) and TNFα levels, and partly prevented lipid peroxidation induced by experimental ON. When the pellet of melatonin was implanted at 4 days postinjection of LPS, it completely reversed the decrease in VEPs and PLR. These data suggest that melatonin could be a promising candidate for ON treatment.

Environmental enrichment protects the retina from early diabetic damage in adult rats.

Diabetic retinopathy is a leading cause of reduced visual acuity and acquired blindness. Available treatments are not completely effective. We analyzed the effect of environmental enrichment on retinal damage induced by experimental diabetes in adult Wistar rats. Diabetes was induced by an intraperitoneal injection of streptozotocin. Three days after vehicle or streptozotocin injection, animals were housed in enriched environment or remained in a standard environment. Retinal function (electroretinogram, and oscillatory potentials), retinal morphology, blood-retinal barrier integrity, synaptophysin, astrocyte and Müller cell glial fibrillary acidic protein, vascular endothelial growth factor, tumor necrosis factor-α, and brain-derived neurotrophic factor levels, as well as lipid peroxidation were assessed in retina from diabetic animals housed in standard or enriched environment. Environmental enrichment preserved scotopic electroretinogram a-wave, b-wave and oscillatory potential amplitude, avoided albumin-Evan's blue leakage, prevented the decrease in retinal synaptophysin and astrocyte glial fibrillary acidic protein levels, the increase in Müller cell glial fibrillary acidic protein, vascular endothelial growth factor and tumor necrosis factor-α levels, as well as oxidative stress induced by diabetes. In addition, enriched environment prevented the decrease in retinal brain-derived neurotrophic factor levels induced by experimental diabetes. When environmental enrichment started 7 weeks after diabetes onset, retinal function was significantly preserved. These results indicate that enriched environment could attenuate the early diabetic damage in the retina from adult rats.

L-Phenylalanine Transport in Saccharomyces cerevisiae: Participation of GAP1, BAP2, and AGP1.

We focused on the participation of GAP1, BAP2, and AGP1 in L-phenylalanine transport in yeast. In order to study the physiological functions of GAP1, BAP2, and AGP1 in L-phenylalanine transport, we examined the kinetics, substrate specificity, and regulation of these systems, employing isogenic haploid strains with the respective genes disrupted individually and in combination. During the characterization of phenylalanine transport, we noted important regulatory phenomena associated with these systems. Our results show that Agp1p is the major transporter of the phenylalanine in a gap1 strain growing in synthetic media with leucine present as an inducer. In a wild type strain grown in the presence of leucine, when ammonium ion was the nitrogen source, Bap2p is the principal phenylalanine carrier.

Global and ocular hypothermic preconditioning protect the rat retina from ischemic damage.

Retinal ischemia could provoke blindness. At present, there is no effective treatment against retinal ischemic damage. Strong evidence supports that glutamate is implicated in retinal ischemic damage. We investigated whether a brief period of global or ocular hypothermia applied 24 h before ischemia (i.e. hypothermic preconditioning, HPC) protects the retina from ischemia/reperfusion damage, and the involvement of glutamate in the retinal protection induced by HPC. For this purpose, ischemia was induced by increasing intraocular pressure to 120 mm Hg for 40 min. One day before ischemia, animals were submitted to global or ocular hypothermia (33°C and 32°C for 20 min, respectively) and fourteen days after ischemia, animals were subjected to electroretinography and histological analysis. Global or ocular HPC afforded significant functional (electroretinographic) protection in eyes exposed to ischemia/reperfusion injury. A marked alteration of the retinal structure and a decrease in retinal ganglion cell number were observed in ischemic retinas, whereas global or ocular HPC significantly preserved retinal structure and ganglion cell count. Three days after ischemia, a significant decrease in retinal glutamate uptake and glutamine synthetase activity was observed, whereas ocular HPC prevented the effect of ischemia on these parameters. The intravitreal injection of supraphysiological levels of glutamate induced alterations in retinal function and histology which were significantly prevented by ocular HPC. These results support that global or ocular HPC significantly protected retinal function and histology from ischemia/reperfusion injury, probably through a glutamate-dependent mechanism.

Therapeutic efficacy of melatonin in reducing retinal damage in an experimental model of early type 2 diabetes in rats.

Diabetic retinopathy (DR) is a leading cause of acquired blindness in adults, mostly affected by type 2 diabetes mellitus (T2DM). We have developed an experimental model of early T2DM in adult rats which mimics some features of human T2DM at its initial stages and provokes significant retinal alterations. The aim of this work was to analyze the effect of melatonin on retinal changes induced by the moderate metabolic derangement. For this purpose, adult male Wistar rats received a control diet or 30% sucrose in the drinking water. Three weeks after this treatment, animals were injected with vehicle or streptozotocin (STZ, 25 mg/kg). One day or 3 wk after vehicle or STZ injection, animals were subcutaneously implanted with a pellet of melatonin. Fasting and postprandial glycemia, and glucose, and insulin tolerance tests were analyzed. At 12 wk of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in metabolic tests, as compared with control groups. Melatonin, which did not affect glucose metabolism in control or diabetic rats, prevented the decrease in the electroretinogram a-wave, b-wave, and oscillatory potential amplitude, and the increase in retinal lipid peroxidation, NOS activity, TNFα, Müller cells glial fibrillary acidic protein, and vascular endothelial growth factor levels. In addition, melatonin prevented the decrease in retinal catalase activity. These results indicate that melatonin protected the retina from the alterations observed in an experimental model of DR associated with type 2 diabetes.

Ischemic conditioning protects the rat retina in an experimental model of early type 2 diabetes.

Diabetic retinopathy is a leading cause of acquired blindness in adults, mostly affected by type 2 diabetes mellitus (T2DM). We have developed an experimental model of early T2DM in adult rats which mimics some features of human T2DM at its initial stages, and provokes significant retinal alterations. We investigated the effect of ischemic conditioning on retinal changes induced by the moderate metabolic derangement. For this purpose, adult male Wistar rats received a control diet or 30% sucrose in the drinking water, and 3 weeks after this treatment, animals were injected with vehicle or streptozotocin (STZ, 25mg/kg). Retinal ischemia was induced by increasing intraocular pressure to 120 mm Hg for 5 min; this maneuver started 3 weeks after vehicle or STZ injection and was weekly repeated in one eye, while control eyes were submitted to a sham procedure. Fasting and postprandial glycemia, and glucose, and insulin tolerance tests were analyzed. At 12 weeks of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in metabolic tests, as compared with control groups. Brief ischemia pulses in one eye and a sham procedure in the contralateral eye did not affect glucose metabolism in control or diabetic rats. Ischemic pulses reduced the decrease in the electroretinogram a-wave, b-wave, and oscillatory potential amplitude, and the increase in retinal lipid peroxidation, NOS activity, TNFα, Müller cells glial fibrillary acidic protein, and vascular endothelial growth factor levels observed in diabetic animals. In addition, ischemic conditioning prevented the decrease in retinal catalase activity induced by T2DM. These results indicate that induction of ischemic tolerance could constitute a fertile avenue for the development of new therapeutic strategies to treat diabetic retinopathy associated with T2DM.

Post-ischemic environmental enrichment protects the retina from ischemic damage in adult rats.

The aim of this study was to elucidate whether post-ischemic enriched environment (EE) housing protects the retina from ischemic damage in adult rats, and the involvement of glutamate in retinal protection induced by EE housing. For this purpose, ischemia was induced by increasing intraocular pressure to 120 mm Hg for 40 min. After ischemia, animals were housed in a standard environment (SE) or EE and subjected to electroretinography and histological analysis. EE housing afforded significant functional protection in eyes exposed to ischemia/reperfusion injury. A marked reduction in retinal thickness and ganglion cell number, and an increase in Müller cell glial fibrillary acidic protein (GFAP) levels were observed in ischemic retinas from SE-housed animals, which were reversed by EE housing. A deficit in anterograde transport from the retina to the superior colliculus was observed in SE- but not in EE-housed animals. In SE-housed animals, ischemia induced a significant decrease in retinal glutamate uptake and glutamine synthetase activity, whereas EE housing reversed the effect of ischemia on these parameters. The intravitreal injection of supraphysiological levels of glutamate partially reproduced retinal alterations induced by ischemia/reperfusion, which were abrogated by EE housing. These results indicate that EE housing significantly protected retinal function and histology from ischemia/reperfusion injury in adult rats, likely through a glutamate-dependent mechanism.

Occupational health and safety experiences among self-identified immigrant workers living or working in Somerville, MA by ethnicity, years in the US, and English proficiency.

In this community based research initiative, we employed a survey instrument predominately developed and administered by Teen Educators to assess occupational health risks for Haitian, Salvadoran, and Brazilian immigrants (n = 405) in Somerville, MA, USA. We demonstrate that a combined analysis of ethnicity, years in the US, and English proficiency better characterized the occupational experience of immigrant workers than considering these variables individually. While years in the US (negatively) and English proficiency (positively) explained the occurrence of health risks, the country of origin identified the most vulnerable populations in the community. Brazilians, Salvadorans, and other Hispanic, all of whom who have been in the US varying length of time, with varying proficiency in English language had twice the odds of reporting injuries due to work compared to other immigrants. Although this observation was not significant it indicates that years in the US and English proficiency alone do not predict health risks among this population. We recommend the initiation of larger studies employing c community based participatory research methods to confirm these differences and to further explore work and health issues of immigrant populations. This study is one of the small number of research efforts to utilize a contemporaneous assessment of occupational health problems in three distinct immigrant populations at the community level within a specific Environmental Justice context and social milieu.

Retinal changes in an experimental model of early type 2 diabetes in rats characterized by non-fasting hyperglycemia.

Diabetic retinopathy is a leading cause of acquired blindness in young, but also in elder adults, mostly affected by type 2 diabetes mellitus (T2DM). The aim of this work was to develop an experimental model of early human T2DM in adult rats, and to analyze retinal functional, morphological, and biochemical changes arising during the early stages of the moderate metabolic derangement. For this purpose, animals were divided in four groups: adult male Wistar rats receiving: tap water and citrate buffer i.p. (group 1), tap water with 30% sucrose and citrate buffer i.p. (group 2), tap water and 25mg/kg i.p streptozotocin (STZ, group 3), or 30% sucrose and STZ (group 4). Fasting and postprandial glycemia, fructosamine and serum insulin levels were assessed. In addition, i.p. glucose and insulin tolerance tests were performed. Retinal function (electroretinogram, ERG) and morphology (optical microscopy), retinal nitric oxide synthase (NOS) activity (using (3)H-arginine), lipid peroxidation (thiobarbituric acid reactive substances, TBARS), and TNFα levels (ELISA) were evaluated. At 6 and 12 weeks of treatment, animals which received a sucrose-enriched diet and STZ showed significant differences in most metabolic tests, as compared with the other groups. At 12 weeks of treatment, a significant decrease in the ERG a- and b- wave and oscillatory potential amplitudes, and a significant increase in retinal NOS activity, TBARS, TNFα, glial fibrillary acidic protein in Müller cells, and vascular endothelial growth factor levels were observed. These results indicate that the combination of diet-induced insulin resistance and a slight secretory impairment resulting from a low-dose STZ treatment mimics some features of human T2DM at its initial stages, and provokes significant retinal alterations.

Bacterial lipopolysaccharide protects the retina from light-induced damage.

Light-induced damage is a widely used model to study retinal degeneration. We examined whether bacterial lipopolysaccharide (LPS) protects the retina against light-induced injury. One day before intense light exposure for 24 h, rats were intravitreally injected with LPS in one eye and vehicle in the contralateral eye. At several time points after light exposure, rats were subjected to electroretinography and histological analysis. Bax, Bcl-xL, p-Akt, and p-Stat3 levels were assessed by Western blotting, and retinal thiobarbituric acid reactive substances levels were measured as an index of lipid peroxidation. One group of animals received injections of dexamethasone, aminoguanidine (an inducible NOS inhibitor), 5-hydroxydecanoic acid (a mitochondrial K(+) /ATP channel blocker), or wortmannin [a phosphoinositide-3-kinase (PI3K) inhibitor] in order to analyze their effect on the protection induced by LPS. LPS afforded significant morphologic and functional protection in eyes exposed to intense light. Light damage induced an increase in mitochondrial Bax/cytoplasmic Bax ratio, and lipid peroxidation which were prevented by LPS. Dexamethasone and wortmannin (but not aminoguanidine or 5-hydroxydecanoic acid) prevented the effect of LPS. Moreover, wortmannin prevented the effect of LPS on p-Akt levels. These results indicate that LPS provides retinal protection against light-induced stress, probably through a PI3K/Akt-dependent mechanism.

Effect of Angeli's salt on the glutamate/glutamine cycle activity and on glutamate excitotoxicity in the hamster retina.

Glutamate is the main excitatory neurotransmitter in the retina, but it is toxic when present in excessive amounts. It is well known that NO is involved in glutamate excitotoxicity, but information regarding the possibility that NO-related species could reciprocally affect glutamate synaptic levels was not previously provided. The dependence of glutamatergic neurons upon glia via the glutamate/glutamine cycle to provide the precursor for neurotransmitter glutamate is well established. The aim of the present work was to comparatively analyze the effect of nitroxyl and NO on the retinal glutamate/glutamine cycle in vitro activity. For this purpose, Angeli's salt (AS) and diethylamine NONOate (DEA/NO) were used as nitroxyl and NO donor, respectively. AS and DEA/NO significantly decreased retinal l-glutamate uptake and glutamine synthetase activity, but only AS decreased l-glutamine influx. Dithiothreitol prevented all the effects of AS and DEA/NO. The intravitreal injection of DEA/NO (but not AS) or a supraphysiological concentration of glutamate induced retinal histological alterations. Although AS could increase glutamate synaptic concentration in vitro, the histological alterations induced by glutamate were abrogated by AS. These results suggest that nitroxyl could regulate the hamster retinal glutamatergic pathway by acting through differential mechanisms at pre- and postsynaptic level.

Ischemic tolerance protects the rat retina from glaucomatous damage.

Glaucoma is a leading cause of acquired blindness which may involve an ischemic-like insult to retinal ganglion cells and optic nerve head. We investigated the effect of a weekly application of brief ischemia pulses (ischemic conditioning) on the rat retinal damage induced by experimental glaucoma. Glaucoma was induced by weekly injections of chondroitin sulfate (CS) in the rat eye anterior chamber. Retinal ischemia was induced by increasing intraocular pressure to 120 mmHg for 5 min; this maneuver started after 6 weekly injections of vehicle or CS and was weekly repeated in one eye, while the contralateral eye was submitted to a sham procedure. Glaucoma was evaluated in terms of: i) intraocular pressure (IOP), ii) retinal function (electroretinogram (ERG)), iii) visual pathway function (visual evoked potentials, (VEPs)) iv) histology of the retina and optic nerve head. Retinal thiobarbituric acid substances levels were assessed as an index of lipid peroxidation. Ischemic conditioning significantly preserved ERG, VEPs, as well as retinal and optic nerve head structure from glaucomatous damage, without changes in IOP. Moreover, ischemia pulses abrogated the increase in lipid peroxidation induced by experimental glaucoma. These results indicate that induction of ischemic tolerance could constitute a fertile avenue for the development of new therapeutic strategies in glaucoma treatment.

Induction of ischemic tolerance protects the retina from diabetic retinopathy.

Diabetic retinopathy is a leading cause of acquired blindness. Available treatments are not very effective. We investigated the effect of a weekly application of retinal ischemia pulses (ischemic conditioning) on retinal damage induced by experimental diabetes. Diabetes was induced by an intraperitoneal injection of streptozotocin. Retinal ischemia was induced by increasing intraocular pressure to 120 mmHg for 5 minutes; this maneuver started 3 days after streptozotocin injection and was weekly repeated in one eye, whereas the contralateral eye was submitted to a sham procedure. Diabetic retinopathy was evaluated in terms of i) retinal function (electroretinogram and oscillatory potentials), ii) integrity of blood-retinal barrier (by albumin-Evans blue complex leakage and astrocyte glial fibrillary acidic protein IHC), iii) optical and electron microscopy histopathologic studies, and iv) vascular endothelial growth factor levels (using Western blot analysis and IHC). Brief ischemia pulses significantly preserved electroretinogram a- and b-wave and oscillatory potentials, avoided albumin-Evans blue leakage, prevented the decrease in astrocyte glial fibrillary acidic protein levels, reduced the appearance of retinal edemas, and prevented the increase in vascular endothelial growth factor levels induced by experimental diabetes. When the application of ischemia pulses started 6 weeks after diabetes onset, retinal function was significantly preserved. These results indicate that induction of ischemic tolerance could constitute a fertile avenue for the development of new therapeutic strategies for diabetic retinopathy treatment.

Melatonin: a novel neuroprotectant for the treatment of glaucoma.

Glaucoma is a leading cause of blindness. Although ocular hypertension is the most important risk factor, several concomitant factors such as elevation of glutamate and decrease in gamma-aminobutyric acid (GABA) levels, disorganized NO metabolism, and oxidative damage could significantly contribute to the neurodegeneration. The aim of this report was to analyze the effect of melatonin on retinal glutamate clearance, GABA concentrations, NO synthesis, and retinal redox status, as well as on functional and histological alterations provoked by chronic ocular hypertension induced by intracameral injections of hyaluronic acid (HA) in the rat eye. In normal retinas, melatonin increased glutamate uptake, glutamine synthase activity, GABA turnover rate, glutamic acid decarboxylase activity, superoxide dismutase activity, and reduced glutathione (GSH) levels, whereas it decreased NOS activity, L-arginine uptake, and lipid peroxidation. To assess the effect of melatonin on glaucomatous neuropathy, weekly injections of HA were performed in the eye anterior chamber. A pellet of melatonin was implanted subcutaneously 24 hr before the first injection or after six weekly injections of HA. Melatonin, which did not affect intraocular pressure (IOP), prevented and reversed the effect of ocular hypertension on retinal function (assessed by electroretinography) and diminished the vulnerability of retinal ganglion cells to the deleterious effects of ocular hypertension. These results indicate that melatonin could be a promissory resource in the management of glaucoma.