Academic literature on the topic 'Retinal excitotoxicity'

Polyamine oxidation plays a major role in neurodegenerative diseases. Previous studies from our laboratory demonstrated that spermine oxidase (SMOX, a member of the polyamine oxidase family) inhibition using MDL 72527 reduced neurodegeneration in models of retinal excitotoxicity and diabetic retinopathy. However, the mechanisms behind the neuroprotection offered by SMOX inhibition are not completely studied. Utilizing the experimental model of retinal excitotoxicity, the present study determined the impact of SMOX blockade in retinal neuroinflammation. Our results demonstrated upregulation in the number of cells positive for Iba-1 (ionized calcium-binding adaptor molecule 1), CD (Cluster Differentiation) 68, and CD16/32 in excitotoxicity-induced retinas, while MDL 72527 treatment reduced these changes, along with increases in the number of cells positive for Arginase1 and CD206. When retinal excitotoxicity upregulated several pro-inflammatory genes, MDL 72527 treatment reduced many of them and increased anti-inflammatory genes. Furthermore, SMOX inhibition upregulated antioxidant signaling (indicated by elevated Nrf2 and HO-1 levels) and reduced protein-conjugated acrolein in excitotoxic retinas. In vitro studies using C8-B4 cells showed changes in cellular morphology and increased reactive oxygen species formation in response to acrolein (a product of SMOX activity) treatment. Overall, our findings indicate that the inhibition SMOX pathway reduced neuroinflammation and upregulated antioxidant signaling in the retina.

Excitotoxicity has been proposed to play a pivotal role in retinal ischemia. Retinal ischemia-associated ocular disorders are vision threatening. The aim was to also examine whether and how S-allyl L-cysteine (SAC) can protect the retina against kainate excitotoxicity. In vivo retinal excitotoxicity was induced by an intravitreous injection of 100 μM kainate into a Wistar rat eye for 1 day. The management and mechanisms involved in the processes were evaluated by electrophysiology, immunohistochemistry, histopathology, and various biochemical approaches. In the present study, the cultured retinal cells were shown to possess kainate receptors. The defined retinal excitotoxic changes were characterized by a decrease in electroretinogram (ERG) b-wave amplitudes, a loss of the fluorogold retrograde labeled retinal ganglion cells (RGCs), an increase in the apoptotic cells in the RGC layer, and an increase in vimentin or glial fibrillary acidic protein (GFAP) immunoreactivity, a marker for Müller cells. An up-regulation in the mRNA levels of inducible nitric oxide synthase (iNOS) and matrix metalloproteinases-9 (MMPs-9) was also detected in the retina subjected to kainate excitoxicity. Importantly, the excitotoxicity-induced alterations were significantly blunted when 100 μM SAC and/or the kainate receptor antagonist CNQX was applied. Conclusively, SAC would seem to protect the retina against kainate excitotoxicity via an inhibition of the up-regulation of iNOS and MMP-9 as well as a modulation of glial activation and apoptosis.

The neurotransmitter glutamate causes excitotoxicity in the human retina. In neonatal rats, the degree of glutamate-induced retinal damage depends on age at administration. To elucidate the sensitivity to glutamate on various developing stage of retina, we investigated glutamate-induced retinal damage and glutamate target cells on each postnatal day (PND). Newborn rats received a single subcutaneous administration of l-glutamate on PNDs 1 to 14. Retinal cell apoptosis characterized as pyknotic and terminal deoxynucleotidyl transferase–mediated dUTP digoxigenin nick end labeling–positive nuclei was analyzed at 6 hr after treatment, and sequential morphological features of retina were evaluated on PND 21. The inner retina on PND 21 exhibited thinning in rats treated after PND 2. The thinning was most severe in rats treated on PND 8 and the number of apoptotic cells also peaked. No thinning was observed in rats treated on PND 14. In the inner nuclear layer, glutamate target cells were mainly amacrine cells; additionally, bipolar cells and horizontal cells were damaged on PND 8. These retinal changes were more severe in central retina than those in peripheral retina on PND 8. Our findings indicate the morphological consequences of glutamate-induced retinal excitotoxicity and glutamate target cells on each PND and reveal that glutamate-induced retinal damage depends on developing stage.

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

We studied short- and long-term effects of intravitreal injection of N-methyl-d-aspartate (NMDA) on melanopsin-containing (m+) and non-melanopsin-containing (Brn3a+) retinal ganglion cells (RGCs). In adult SD-rats, the left eye received a single intravitreal injection of 5µL of 100nM NMDA. At 3 and 15 months, retinal thickness was measured in vivo using Spectral Domain-Optical Coherence Tomography (SD-OCT). Ex vivo analyses were done at 3, 7, or 14 days or 15 months after damage. Whole-mounted retinas were immunolabelled for brain-specific homeobox/POU domain protein 3A (Brn3a) and melanopsin (m), the total number of Brn3a+RGCs and m+RGCs were quantified, and their topography represented. In control retinas, the mean total numbers of Brn3a+RGCs and m+RGCs were 78,903 ± 3572 and 2358 ± 144 (mean ± SD; n = 10), respectively. In the NMDA injected retinas, Brn3a+RGCs numbers diminished to 49%, 28%, 24%, and 19%, at 3, 7, 14 days, and 15 months, respectively. There was no further loss between 7 days and 15 months. The number of immunoidentified m+RGCs decreased significantly at 3 days, recovered between 3 and 7 days, and were back to normal thereafter. OCT measurements revealed a significant thinning of the left retinas at 3 and 15 months. Intravitreal injections of NMDA induced within a week a rapid loss of 72% of Brn3a+RGCs, a transient downregulation of melanopsin expression (but not m+RGC death), and a thinning of the inner retinal layers.

One of the causes of nervous system degeneration is an excess of glutamate released upon several diseases. Glutamate analogs, like N-methyl-DL-aspartate (NMDA) and kainic acid (KA), have been shown to induce experimental retinal neurotoxicity. Previous results have shown that NMDA/KA neurotoxicity induces significant changes in the full field electroretinogram response, a thinning on the inner retinal layers, and retinal ganglion cell death. However, not all types of retinal neurons experience the same degree of injury in response to the excitotoxic stimulus. The goal of the present work is to address the effect of intraocular injection of different doses of NMDA/KA on the structure and function of several types of retinal cells and their functionality. To globally analyze the effect of glutamate receptor activation in the retina after the intraocular injection of excitotoxic agents, a combination of histological, electrophysiological, and functional tools has been employed to assess the changes in the retinal structure and function. Retinal excitotoxicity caused by the intraocular injection of a mixture of NMDA/KA causes a harmful effect characterized by a great loss of bipolar, amacrine, and retinal ganglion cells, as well as the degeneration of the inner retina. This process leads to a loss of retinal cell functionality characterized by an impairment of light sensitivity and visual acuity, with a strong effect on the retinal OFF pathway. The structural and functional injury suffered by the retina suggests the importance of the glutamate receptors expressed by different types of retinal cells. The effect of glutamate agonists on the OFF pathway represents one of the main findings of the study, as the evaluation of the retinal lesions caused by excitotoxicity could be specifically explored using tests that evaluate the OFF pathway.

In the physiological condition, glutamate acts as an excitatory neurotransmitter in the retina. However, excessive glutamate can be toxic to retinal neurons by overstimulation of the glutamate receptors. Glutamate excess is primarily attributed to perturbation in the homeostasis of the glutamate metabolism. Major pathway of glutamate metabolism consists of glutamate uptake by glutamate transporters followed by enzymatic conversion of glutamate to nontoxic glutamine by glutamine synthetase. Glutamate metabolism requires energy supply, and the energy loss inhibits the functions of both glutamate transporters and glutamine synthetase. In this review, we describe the present knowledge concerning the retinal glutamate metabolism under the physiological and pathological conditions.

Iron is essential for retinal metabolism, but an excess of ferrous iron causes oxidative stress. In glaucomatous eyes, retinal ganglion cell (RGC) death has been associated with dysregulation of iron homeostasis. Transferrin (TF) is an endogenous iron transporter that controls ocular iron levels. Intraocular administration of TF is neuroprotective in various models of retinal degeneration, preventing iron overload and reducing iron-induced oxidative stress. Herein, we assessed the protective effects of TF on RGC survival, using ex vivo rat retinal explants exposed to iron, NMDA-induced excitotoxicity, or CoCl2-induced hypoxia, and an in vivo rat model of ocular hypertension (OHT). TF significantly preserved RGCs against FeSO4-induced toxicity, NMDA-induced excitotoxicity, and CoCl2-induced hypoxia. TF protected RGCs from apoptosis, ferroptosis, and necrosis. In OHT rats, TF reduced RGC loss by about 70% compared to vehicle-treated animals and preserved about 47% of the axons. Finally, increased iron staining was shown in the retina of a glaucoma patient’s eye as compared to non-glaucomatous eyes. These results indicate that TF can interfere with different cell-death mechanisms involved in glaucoma pathogenesis and demonstrate the ability of TF to protect RGCs exposed to elevated IOP. Altogether, these results suggest that TF is a promising treatment against glaucoma neuropathy.

Kwong Man Kwong.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1997.
Includes bibliographical references (leaves 83-99).
TABLE OF CONTENTS --- p.i
ACKNOWLEDGEMENTS --- p.vi
LIST OF FIGURES --- p.vii
LIST OF ABBREVIATIONS --- p.ix
Chapter I. --- ABSTRACT --- p.1
Chapter II. --- INTRODUCTION --- p.4
Chapter III. --- LITERATURE REVIEW --- p.6
Chapter A. --- EXCITATORY AMINO ACIDS AND EXCITOTOXICITY --- p.6
Chapter 1. --- GLUTAMATE RECEPTORS --- p.7
Chapter 2. --- NMDA RECEPTOR --- p.9
Chapter 3. --- EXCITOTOXICITY --- p.10
Chapter a. --- ACUTE PHASE --- p.10
Chapter b. --- DELAYED PHASE --- p.11
Chapter c. --- MECHANISM --- p.11
Chapter i) --- Inhibition of Na+，K+-ATPase --- p.12
Chapter ii) --- Impaired Mitochondrial Calcium Buffering --- p.12
Chapter iii) --- Perturbation of Cytoskeletal Organisation --- p.13
Chapter iv) --- Phospholipase Activation --- p.14
Chapter v) --- Endonuclease Activation --- p.15
Chapter vi) --- Protein Kinase C Activation --- p.15
Chapter vii) --- Xanthine Oxidase Activation --- p.16
Chapter viii) --- Nitric Oxidase Synthase Activation --- p.16
Chapter B. --- APOPTOSIS --- p.19
Chapter 1. --- MORPHOLOGICAL CHANGES --- p.19
Chapter 2. --- BIOCHEMICAL AND MOLECULAR CHANGES --- p.20
Chapter 3. --- APOPTOTIC MEDIATORS --- p.21
Chapter a. --- INTERLEUKIN-1β CONVERTING ENZYME (ICE) --- p.21
Chapter b. --- ENDONUCLEASE --- p.22
Chapter c. --- NITRIC OXIDE SYNTHASE (NOS) --- p.23
Chapter d. --- POLY(ADP-RIBOSE) POLYMERASE (PARP) --- p.24
Chapter e. --- CALPAINS --- p.25
Chapter IV. --- NMDA INDUCED APOPTOSIS IN RAT RETINA --- p.27
Chapter A. --- RATIONALE --- p.27
Chapter B. --- MATERIALS AND METHODS --- p.31
Chapter 1. --- NMDA INDUCED EXCITOTOXICITY --- p.31
Chapter a. --- INTRAVITREAL INJECTIONS --- p.31
Chapter b. --- RETINAL GANGLION CELL COUNTS (RGCC) --- p.32
Chapter i) --- Flat Preparation of Rat Retina --- p.33
Chapter ii) --- RGCC --- p.33
Chapter d. --- INNER RETINAL THICKNESS (IRT) --- p.34
Chapter i. --- Preparation of Epoxyl Specimens --- p.34
Chapter ii. --- Measurement of IRT --- p.36
Chapter 2. --- DOSE RESPONSE STUDY OF NMDA --- p.36
Chapter 3. --- NMDA INDUCED APOPTOSIS IN RAT RETINA --- p.37
Chapter a. --- GEL ELECTROPHORESIS OF RETINAL DNA --- p.37
Chapter b. --- HISTOPATHOLOGICAL STUDIES --- p.39
Chapter i) --- Light Microscopy --- p.39
Chapter ii) --- Terminal Deoxynucleotidyl Transferase-mediated dUTP-biotin Nick End Labelling (TUNEL) --- p.40
Chapter iii) --- Electron Microscopy (EM) --- p.41
Chapter c. --- MORPHOMETRY --- p.41
Chapter i) --- TUNEL Positive Nuclei --- p.41
Chapter ii) --- RGCC and IRT --- p.42
Chapter 4. --- STUDY OF ENZYME INHIBITORS --- p.42
Chapter C. --- RESULTS --- p.43
Chapter 1. --- EXCITOTOXICITY IN RAT RETINA --- p.43
Chapter a. --- RGCC --- p.43
Chapter b. --- IRT --- p.44
Chapter 2. --- DOSE DEPENDENT TISSUE RESPONSES AND REGIONAL RESPONSES --- p.44
Chapter a. --- RGCC --- p.44
Chapter b. --- IRT --- p.45
Chapter 3. --- NMDA INDUCED APOPTOSIS IN RAT RETINA --- p.45
Chapter a. --- RETINAL DNA GEL ELECTROPHORESIS --- p.46
Chapter b. --- HISTOPATHOLOGY AND TUNEL --- p.46
Chapter c. --- MORPHOMETRY OF TUNEL AT THE RGCL AND INL --- p.47
Chapter d. --- TISSUE RESPONSES AT 7 DAYS AFTER INJECTION --- p.48
Chapter e. --- EM --- p.48
Chapter i) --- RGCL --- p.48
Chapter ii) --- INL --- p.48
Chapter 4. --- ENZYME INHIBITOR STUDY IN NMDA INDUCED EXCITOTOXICITY --- p.49
Chapter a. --- EFFECT OF VARIOUS ENZYME INHIBITORS ON RGCC --- p.49
Chapter b. --- EFFECT OF VARIOUS ENZYME INHIBITORS ON IRT --- p.50
Chapter D. --- DISCUSSION --- p.51
Chapter 1. --- NMDA INDUCED EXCITOTOXICITY IN RAT RETINA --- p.51
Chapter 2. --- DOSE DEPENDENT RESPONSES AND REGIONAL RESPONSES --- p.55
Chapter 3. --- NMDA INDUCED APOPTOSIS IN RAT RETINA --- p.58
Chapter 4. --- INHIBITOR STUDY --- p.62
Chapter a. --- ICE --- p.63
Chapter b. --- ENDONUCLEASE --- p.65
Chapter c. --- NOS --- p.67
Chapter d. --- PARP --- p.69
Chapter e. --- CALPAIN --- p.70
Chapter V. --- NMDA INDUCED APOPTOSIS IN RABBIT RETINA --- p.72
Chapter A. --- RATIONALE --- p.72
Chapter B. --- MATERIALS AND METHODS --- p.73
Chapter 1. --- INTRAVITREAL INJECTION OF NMDA --- p.73
Chapter 2. --- HISTOPATHOLOGY AND TUNEL --- p.74
Chapter 3. --- MORPHOMETRY OF TUNEL --- p.74
Chapter 4. --- TISSUE RESPONSES AT 7 DAYS AFTER INJECTION --- p.74
Chapter a. --- RGCC --- p.74
Chapter b. --- IRT --- p.74
Chapter 5. --- EM --- p.75
Chapter C. --- RESULTS --- p.76
Chapter 1. --- HISTOPATHOLOGY AND TUNEL --- p.76
Chapter 2. --- MORPHOMETRY OF TUNEL --- p.77
Chapter 3. --- TISSUE RESPONSES AT 7 DAYS POST INJECTION --- p.78
Chapter a. --- RGCC --- p.78
Chapter b. --- IRT --- p.78
Chapter 4. --- EM --- p.79
Chapter a. --- RGCL --- p.79
Chapter b. --- INL --- p.79
Chapter B. --- DISCUSSION --- p.80
Chapter VI. --- CONCLUSION --- p.82
Chapter VII. --- REFERENCES --- p.83
Chapter VIII. --- FIGURES --- p.100

Studies concerning retinal neurodegeneration have increased remarkably over recent decades as efforts have focused on elucidating mechanisms of damage and ways to halt the degenerative progression. The retina is a complex structure that consists of multiple layers of different types of neurons. The retinal ganglion cell (RGC) layer is particularly susceptible to damage and its degeneration is a feature of conditions such as glaucoma. In addition to well-described mechanisms of retinal neuron injury in glaucoma, such as mitochondrial dysfunction and oxidative stress, energetic failure has also been postulated. In this thesis, emphasis is directed towards investigating the retinal effects of creatine, which has been postulated to act by overcoming tissue bioenergetic failure, in culture and animal models of metabolic dysfunction. There are two papers to this thesis. The first paper characterizes various markers of RGC in a well-known model of retinal ganglion cell injury – N-methyl- D-aspartate (NMDA)-induced retinal excitotoxicity. As there exists no gold standard marker for RGC for the purposes of neuroprotection studies, we aimed to compare four recent ganglion cell markers by retinal whole-mount immunohistochemistry and observe how they changed over time following NMDA exposure. We found that NMDA-induced RGC injury was maximal within the first 24 hours of exposure and there is good consistency between markers Brn3a, RBPMS and γ-synuclein. Of all markers tested, Brn3a was the most useful marker of RGCs to employ in studies looking at loss and counteraction of loss for these cells. This finding was immediately employed for the in vivo work in the second study. The second paper addresses the effects of creatine in models of retinal injury both in vitro and in vivo. Firstly, a rat retinal culture model of energetic dysfunction using sodium azide was used. Levels of apoptosis, ATP and reactive oxygen species were also tested. Creatine was found to partially protect cultured rat retinal neurons from energetic failure, as well as reducing oxidative stress and apoptosis. The study then moved on to in vivo experiments whereby effects of oral creatine supplementation in rat models of NMDA-induced retinal excitotoxicity and retinal ischaemia were examined. RGC reductions were found to be up to 70% but these losses were not significantly reduced by creatine supplementation. When apoptotic levels were assessed, there remained no significant difference between the creatine-fed and control group of rats that underwent NMDA-induced retinal toxicity. Further studies, especially on the mechanisms of creatine neuroprotection, would need to be performed to explain the discrepancy in the ability of this compound to provide neuroprotection in vitro but not in vivo.
Thesis (MPhil) -- University of Adelaide, Adelaide Medical School, 2018

A large body of evidence supports the notion that excitotoxicity plays a major role in the pathogenesis of a number of neurological diseases, including central nervous system (CNS) ischaemia, Alzheimer's disease, motor neurone disease, and glaucoma. In the global population 60 years of age and over, these diseases are among the leading causes of mortality and morbidity. Although the site of excitotoxic injury is principally at the level of the cell body (perikaryal), understanding the secondary effects on the neuronal axon is important because axonopathy is a documented early feature of these common neurological conditions; hence, an understanding of the pattern and mechanisms of secondary axonal degeneration after excitotoxic perikaryal injury could provide novel detection and treatment strategies in the early phase of neurological disease. The retina and optic nerve, as approachable regions of the CNS, provide a unique anatomical substrate to investigate axonal degeneration after perikaryal excitotoxic injury. Spatiotemporal changes in the retina and optic nerve were studied after injection of 20nM of Nmethyl-D-Aspartate (NMDA) in the left eye of the rat with the saline-injected right eye serving as the control. Temporal changes in the morphology of retina and optic nerve were studied by light and electron microscopy. Progressive retinal damage beginning at 72 hrs, seen as thinning of the inner retina and cell loss in the ganglion cell layer, showed strong correlation (R= 0.949) with degenerative changes in the optic nerve; the distal optic nerve segment displayed significantly more axon loss, axon swellings and myelin damage than the proximal segment (p<0.05), suggestive of a 'dying-back type degeneration'. Beginning at 24 hrs, electron microscopy demonstrated various features of necrosis in retinal ganglion cells (RGCs): mitochondrial and endoplasmic reticulum swelling, disintegration of polyribosomes, rupture of membranous organelle and formation of myelin bodies. Ultrastructural damage in the optic nerve, which began at 72 hrs, mimicked the changes of Wallerian degeneration, where early nodal-paranodal disturbances were followed by the appearance of three major morphological variants: watery degeneration, dark degeneration, and demyelination. Features suggestive of RGC regeneration in the form of dendritic sprouting after acute excitotoxic injury were also demonstrated at day 7. Immunohistochemistry revealed glial cell responses and changes to the axon transport system. Excitotoxic injury resulted in progressive activation of macroglia (Müller cells and astrocytes) and microglial cells in the retina and optic nerve as demonstrated by increased glial-fibrillary-acidic protein (GFAP) and ED-1 immunolabelling as early as 72 hrs. Interxonal glial cells in the optic nerve also showed increased β-amyloid precursor protein (β-APP) beginning at 72 hrs. Impairment of slow axonal transport at 72 hrs resulted in decrease anterograde transport of neurofilament-light (NF-L) to the axon terminal and hence their accumulation in proximal neuron (seen as NF-L rich spheroids). This fundamental research revealed a pathological picture of Wallerian-like degeneration after perikaryal excitotoxic injury in the CNS. This novel finding is consistent with recent evidence of a labile axonal 'survival' factor, nicotinamide mononucleotide adenylyltransferase 2,(Nmnat2) produced by the neuronal cell body. Further study is required to test the hypothesis that a lack of Nmnat2 is the mechanism by which axons degenerate after excitotoxic perikaryal injury.
Thesis (Ph.D.) -- University of Adelaide, School of Medicine, 2011

Sun Qiang.
"December 1999."
Thesis (Ph.D.)--Chinese University of Hong Kong, 1999.
Includes bibliographical references (p. 119-139).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Mode of access: World Wide Web.