Survival and axonal regeneration of retinal ganglion cells in adult cats

Intravitreal AAV2 gene delivery to feline retinal ganglion cells

Effective strategies for the neuroprotection and preservation of retinal ganglion cells (RGCs) remain elusive in the management of glaucoma. A spontaneous genetic model of glaucoma has been identified in cats and extensively characterized as a viable translational model, with eye size and anatomy similar to humans. In this study we sought to establish initial proof of concept for gene delivery to feline RGCs via intravitreal injection of AAV2 in normal cats. Pre-retinal, posterior vitreal injection of AAV2/2-CMV-GFP, was performed overlying the area centralis in 5 adult cats. Immunosuppressive oral prednisolone was administered perioperatively and gradually tapered over 6-10wks post-injection. Ophthalmic examination was performed pre- and post-injection. The GFP reporter expression and morphological effects of viral transduction on the retina were monitored in vivo using confocal scanning laser ophthalmoscopy (cSLO) and optical coherence tomography (OCT), respectively (Spectralis OCT-HRA, Heidelberg), at 1-2wk intervals over 6-10wks. Full-field electroretinograms (ERG) and visual evoked potentials (VEP) were recorded at baseline and post-injection. Retinas were examined by histology and immunolabeling for the RGC marker RBPMS and Müller cell and astrocyte marker SOX9, and GFP expression was examined in the retina, optic nerve (ON), optic tract and lateral geniculate nucleus (LGN). GFP+ retinal cells and RGC axons were visualized by cSLO at 1-2 weeks post-injection. No retinal morphological changes were observed by OCT in vivo but 3/5 eyes exhibited mild retinal inflammation on histology. Retinal and ON function were preserved in injected eyes compared to baseline and untreated eyes. GFP expression was predominantly identified in RBPMS+ RGC cells as well as SOX9+ Müller cells. GFP fluorescence was observed throughout RGC nerve fiber tract in the central visual pathway. Peak transduction in RGCs (up to ∼ 20 %) was observed in the regions with high GFP expression, but < 1 % of RGCs expressed GFP across the whole retina. Our data provide proof of concept that pre-retinal injection of AAV2/2 may represent a feasible platform for gene delivery to feline RGCs in vivo but highlight a need for further refinement to improve RGC transduction efficiency and control low-grade retinal inflammation.

Morphological Characteristics of Retinal Ganglion Cells in the Retinas of Giant Pandas (Ailuropoda melanoleuca)

Vision plays a crucial role in the survival of animals, and the visual system has particularly selectively evolved in response to the visual environment, ecological niche, and species habitats in vertebrate species. To date, a horizontal streak of retinal ganglion cell (RGC) distribution pattern is observed across mammal species. Here, we report that the giant panda's vertically oriented visual streak, combined with current evidence of the animal's forward-placed eyes, ocular structure, and retinal neural topographic distribution patterns, presents the emergence of a well-adapted binocular visual system. Our results suggest that the giant panda may use a unique way to processing binocular visual information. Results of mathematical simulation are in favor of this hypothesis. The topographic distribution properties of RGCs reported here could be essential for understanding the visual adaptation and evolution of this living fossil.

Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.

Subtype-specific survival and regeneration of retinal ganglion cells in response to injury

Retinal ganglion cells (RGCs) are a heterogeneous population of neurons that function synchronously to convey visual information through the optic nerve to retinorecipient target areas in the brain. Injury or disease to the optic nerve results in RGC degeneration and loss of visual function, as few RGCs survive, and even fewer can be provoked to regenerate their axons. Despite causative insults being broadly shared, regeneration studies demonstrate that RGC types exhibit differential resilience to injury and undergo selective survival and regeneration of their axons. While most early studies have identified these RGC types based their morphological and physiological characteristics, recent advances in transgenic and gene sequencing technologies have further enabled type identification based on unique molecular features. In this review, we provide an overview of the well characterized RGC types and identify those shown to preferentially survive and regenerate in various regeneration models. Furthermore, we discuss cellular characteristics of both the resilient and susceptible RGC types including the combinatorial expression of different molecular markers that identify these specific populations. Lastly, we discuss potential molecular mechanisms and genes found to be selectively expressed by specific types that may contribute to their reparative capacity. Together, we describe the studies that lay the important groundwork for identifying factors that promote neural regeneration and help advance the development of targeted therapy for the treatment of RGC degeneration as well as neurodegenerative diseases in general.

Calcium in Neuronal and Glial Response to Axotomy

Neurotrauma assumes an instant or delayed disconnection of axons (axotomy), which affects not only neurons, but surrounding glia as well. Not only mechanically injured glia near the site of disconnection, especially transection, is subjected to the damage, but also glia that is remote from the lesion site. Glial cells, which surround the neuronal body, in turn, support neuron survival, so there is a mutual protection between neuron and glia. Calcium signaling is a central mediator of all post-axotomy events, both in neuron and glia, playing a critical role in their survival/regeneration or death/degeneration. The involvement of calcium in post-axotomy survival of the remote, mechanically intact glia is poorly studied. The purpose of this review is to sum up the calcium-involving mechanisms in responses of neurons and glial cells to axotomy to show their importance and to give some suggestions for future research of remote glia in this context.

Commonalities of optic nerve injury and glaucoma-induced neurodegeneration: Insights from transcriptome-wide studies

Glaucoma is a collection of diseases that lead to an irreversible vision loss due to damage of retinal ganglion cells (RGCs). Although the underlying events leading to RGC death are not fully understood, recent research efforts are beginning to define the genetic changes that play a critical role in the initiation and progression of glaucomatous injury and RGC death. Several genetic and experimental animal models have been developed to mimic glaucomatous neurodegeneration. These models differ in many respects but all result in the loss of RGCs. Assessing transcriptional changes across different models could provide a more complete perspective on the molecular drivers of RGC degeneration. For the past several decades, changes in the retinal transcriptome during neurodegeneration process were defined using microarray methods, RNA sequencing and now single cell RNA sequencing. It is understood that these methods have strengths and weaknesses due to technical differences and variations in the analytical tools used. In this review, we focus on the use of transcriptome-wide expression profiling of the changes occurring as RGCs are lost across different glaucoma models. Commonalities of optic nerve crush and glaucoma-induced neurodegeneration are identified and discussed.

It's About Time: Time-Dependent Tissue Damage in the Adult Porcine Retina After Enucleation

The ex vivo large animal retina is extensively used in research ranging from discovery of disease mechanisms to future treatment paradigms. Due to limited standardization when harvesting the tissue, the time after enucleation is often extended for several hours, a factor that so far has not yet been fully characterized. The purpose of this study was to investigate the relationship between time after enucleation and retinal tissue damage. Adult, porcine retinal explants were dissected and fixed 90 or 240 min after enucleation. In a separate experiment, explants were cultured for 48 h, following dissection either 90 or 240 min after enucleation. Retinas were analyzed morphologically using hematoxylin and eosin for overall tissue damage, TUNEL staining for detection of apoptosis, and RBPMS immunohistochemistry for evaluation of ganglion cell survival. In addition, medium from the cultured explants was sampled after 2, 24, and 48 h of culture and assessed for the cell damage marker lactate dehydrogenase (LDH). Retinas examined 240 min after enucleation displayed a significant increase in overall tissue damage, increased apoptosis, and decreased ganglion cell survival compared with 90-min counterparts. In the culture experiment, no significant difference in overall tissue damage was found between the 2 groups, however, apoptosis was significantly increased, and ganglion cell survival decreased in the cultured 240-min group. In addition, a significantly increased LDH medium activity was found in the 240-min group compared with the 90-min counterpart at all time points. The adult porcine retina is relatively resistant to tissue damage 90 min after enucleation but displays distinct signs of injury after 240 min. The importance of these time points is further highlighted when retinal explants are cultured. Our results strongly suggest that time after enucleation is a crucial factor that should be considered in experiments involving the ex vivo adult porcine retina.

Intravitreal quantum dots for retinitis pigmentosa: a first-in-human safety study

Background: Studies indicate that electrical stimulation of retinitis pigmentosa (RP) retina is beneficial. Quantum dots (QDs) can convert light to electrical stimulus and therefore may have therapeutic potential for RP. Methods: This was an open-label, fellow eye-controlled, first-in-human safety study. Five adults with end-stage (arm A) and 15 with severe (arm B) RP received one or two intravitreal injections of 0.2 or 2μM cadmium/selenium 655 Alt QDs. Results: No adverse events were attributed to QDs. In arm A, median best corrected visual acuity was unchanged. In arm B, mean best corrected visual acuity improved from 6/398 to 6/177, versus 6/147 to 6/144 in the fellow eye. Conclusion: Intravitreal QDs can be safely administered to patients with RP. Vision appears to benefit and further validating studies are justified.

Natural Products: Evidence for Neuroprotection to Be Exploited in Glaucoma

Glaucoma, a leading cause of irreversible blindness worldwide, is an optic neuropathy characterized by the progressive death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is recognized as the main risk factor. Despite effective IOP-lowering therapies, the disease progresses in a significant number of patients. Therefore, alternative IOP-independent strategies aiming at halting or delaying RGC degeneration is the current therapeutic challenge for glaucoma management. Here, we review the literature on the neuroprotective activities, and the underlying mechanisms, of natural compounds and dietary supplements in experimental and clinical glaucoma.

Role of glia in optic nerve

Glial cells are critically important for maintenance of neuronal activity in the central nervous system (CNS), including the optic nerve (ON). However, the ON has several unique characteristics, such as an extremely high myelination level of retinal ganglion cell (RGC) axons throughout the length of the nerve (with virtually all fibers myelinated by 7 months of age in humans), lack of synapses and very narrow geometry. Moreover, the optic nerve head (ONH) - a region where the RGC axons exit the eye - represents an interesting area that is morphologically distinct in different species. In many cases of multiple sclerosis (demyelinating disease of the CNS) vision problems are the first manifestation of the disease, suggesting that RGCs and/or glia in the ON are more sensitive to pathological conditions than cells in other parts of the CNS. Here, we summarize current knowledge on glial organization and function in the ON, focusing on glial support of RGCs. We cover both well-established concepts on the important role of glial cells in ON health and new findings, including novel insights into mechanisms of remyelination, microglia/NG2 cell-cell interaction, astrocyte reactivity and the regulation of reactive astrogliosis by mitochondrial fragmentation in microglia.

c-Jun N-terminal kinase 3 deficiency protects axotomized retinal ganglion cells via affecting mitochondria involved apoptosis pathway

AIM

To illustrate the isoform-specific role and mechanism of c-Jun N-terminal kinases (JNKs) in mouse optic nerve axotomy induced neurotrauma.

METHODS

We firstly investigated the expression of JNK1, JNK2, and JNK3 in the retinal ganglion cells (RGCs) by double-immunofluorescent staining. Then we created optic nerve axotomy model in wild type as well as JNK1, JNK2, JNK3, isoform specific gene deficiency mice. With that, we checked the protein expression profile of JNKs and its active form, and quantified the survival RGCs number by immunofluorescence staining. We further explored the molecules underlying isoform specific protective effect by real-time polymerase chain reaction (PCR) and Western blotting assay.

RESULTS

We found that all the three isoforms of JNKs were expressed in the RGCs. Deficiency of JNK3, but not JNK1 or JNK2, significantly alleviated optic nerve axotomy induced RGCs apoptosis. We further established that expression of Noxa, a pro-apoptotic member of BH3 family, was significantly suppressed only in JNK3 gene deficiency mice. But tumor necrosis factor receptor 1 (TNFR1) and Fas, two key modulators of death receptor mediated apoptosis pathway, did not display obvious change in the expression.

CONCLUSION

It is suggested that mitochondria mediated apoptosis, but not death receptor mediated apoptosis got involved in the JNK3 gene deficiency induced RGCs protection. Our study provides a novel insight into the isoform-specific role of JNKs in neurotrauma and indicates some cues for its therapeutics.

Early Postnatal Development of the Lamination in the Lateral Geniculate Nucleus A-Layers in Cats

The early postnatal development of the A-layers of the dorsal lateral geniculate nucleus (LGNd) was investigated in kittens aged 0-34 days by immunohistochemistry for the selective marker for neuronal differentiation (NeuN protein) and parvalbumin. We report two new facts about the LGNd development. First, there is a transient stratification of NeuN labelling in layer A, and to a lesser extent in layer A1, in kittens aged 0 and 4 days. Second, a transient population of large cells that are located between the LGNd A-layers (interlaminar cells) showed high expression levels of both NeuN and parvalbumin. These neurons possessed both the morphological and immunohistochemical features, similar to cells in the neighbouring perigeniculate nucleus. Both NeuN-stratification and double-stained interlaminar cells gradually disappeared during the second postnatal week, and almost completely vanished by the opening of the critical period. We discuss a possible linkage between these observed transitory networks and the ON-/OFF- and X-/Y-cells development and propose that the data obtained reflect the functioning of the early environmentally independent geniculate networks.

Rational Basis for Nutraceuticals in the Treatment of Glaucoma

BACKGROUND

Glaucoma, the second leading cause of blindness worldwide, is a chronic optic neuropathy characterized by progressive retinal ganglion cell (RGC) axons degeneration and death. Primary open-angle glaucoma (OAG), the most common type, is often associated with increased intraocular pressure (IOP), however other factors have been recognized to partecipate to the patogenesis of the optic neuropathy. IOP-independent mechanisms that contribute to the glaucoma-related neurodegeneration include oxidative stress, excitotoxicity, neuroinflammation, and impaired ocular blood flow. The involvement of several and diverse factors is one of the reasons for the progression of glaucoma observed even under efficient IOP control with the currently available drugs.

METHODS

Current research and online content related to the potential of nutritional supplements for limiting retinal damage and improving RGC survival is reviewed.

RESULTS

Recent studies have suggested a link between dietary factors and glaucoma risk. Particularly, some nutrients have proven capable of lowering IOP, increase circulation to the optic nerve, modulate excitotoxicity and promote RGC survival. However, the lack of clinical trials limit their current therapeutic use. The appropriate use of nutraceuticals that may be able to modify the risk of glaucoma may provide insight into glaucoma pathogenesis and decrease the need for, and therefore the side effects from, conventional therapies.

CONCLUSION

The effects of nutrients with anti-oxidant and neuroprotective properties are of great interest and nutraceuticals may offer some therapeutic potential although a further rigorous evaluation of nutraceuticals in the treatment of glaucoma is needed to determine their safety and efficacy.

Molecular genetics and emerging therapies for retinitis pigmentosa: Basic research and clinical perspectives

Retinitis Pigmentosa (RP) is a hereditary retinopathy that affects about 2.5 million people worldwide. It is characterized with progressive loss of rods and cones and causes severe visual dysfunction and eventual blindness in bilateral eyes. In addition to more than 3000 genetic mutations from about 70 genes, a wide genetic overlap with other types of retinal dystrophies has been reported with RP. This diversity of genetic pathophysiology makes treatment extremely challenging. Although therapeutic attempts have been made using various pharmacologic agents (neurotrophic factors, antioxidants, and anti-apoptotic agents), most are not targeted to the fundamental cause of RP, and their clinical efficacy has not been clearly proven. Current therapies for RP in ongoing or completed clinical trials include gene therapy, cell therapy, and retinal prostheses. Gene therapy, a strategy to correct the genetic defects using viral or non-viral vectors, has the potential to achieve definitive treatment by replacing or silencing a causative gene. Among many clinical trials of gene therapy for hereditary retinal diseases, a phase 3 clinical trial of voretigene neparvovec (AAV2-hRPE65v2, Luxturna) recently showed significant efficacy for RPE65-mediated inherited retinal dystrophy including Leber congenital amaurosis and RP. It is about to be approved as the first ocular gene therapy biologic product. Despite current limitations such as limited target genes and indicated patients, modest efficacy, and the invasive administration method, development in gene editing technology and novel gene delivery carriers make gene therapy a promising therapeutic modality for RP and other hereditary retinal dystrophies in the future.

3D Visualization of Individual Regenerating Retinal Ganglion Cell Axons Reveals Surprisingly Complex Growth Paths

Retinal ganglion cells (RGCs), the sole output cells of the retina, are a heterogeneous population of neurons that project axons to visual targets in the brain. Like most CNS neurons, RGCs are considered incapable of mounting long distance axon regeneration. Using immunolabeling-enabled 3D imaging of solvent-cleared organs (iDISCO) in transgenic mice, we tracked the entire paths of individual RGC axons and show that adult RGCs are highly capable of spontaneous long-distance regeneration, even without any treatment. Our results show that the Thy1-H-YFP mouse sparsely labels RGCs, consisting predominantly of regeneration-competent α-type RGCs (αRGCs). Following optic nerve crush, many of the YFP-labeled RGC axons extend considerable distances proximal to the injury site with only a few penetrating through the lesion. This tortuous axon growth proximal to the lesion site is even more striking with intravitreal ciliary neurotrophic factor (CNTF) treatment. We further demonstrate that despite traveling more than 5 mm (i.e., a distance equal to the length of mouse optic nerve), many of these circuitous axons are confined to the injury area and fail to reach the brain. Our results re-evaluate the view that RGCs are naturally incapable of re-extending long axons, and shift the focus from promoting axon elongation, to understanding factors that prevent direct growth of axons through the lesion and the injured nerve.

Control of Retinal Ganglion Cell Positioning and Neurite Growth: Combining 3D Printing with Radial Electrospun Scaffolds

Retinal ganglion cells (RGCs) are responsible for the transfer of signals from the retina to the brain. As part of the central nervous system, RGCs are unable to regenerate following injury, and implanted cells have limited capacity to orient and integrate in vivo. During development, secreted guidance molecules along with signals from extracellular matrix and the vasculature guide cell positioning, for example, around the fovea, and axon outgrowth; however, these changes are temporally regulated and are not the same in the adult. Here, we combine electrospun cell transplantation scaffolds capable of RGC neurite guidance with thermal inkjet 3D cell printing techniques capable of precise positioning of RGCs on the scaffold surface. Optimal printing parameters are developed for viability, electrophysiological function and, neurite pathfinding. Different media, commonly used to promote RGC survival and growth, were tested under varying conditions. When printed in growth media containing both brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor (CNTF), RGCs maintained survival and normal electrophysiological function, and displayed radial axon outgrowth when printed onto electrospun scaffolds. These results demonstrate that 3D printing technology may be combined with complex electrospun surfaces in the design of future retinal models or therapies.

Natural compounds and retinal ganglion cell neuroprotection

Glaucoma, the second leading cause of blindness in the world, is a chronic optic neuropathy often associated with increased intraocular pressure and characterized by progressive retinal ganglion cell (RGC) axons degeneration and death leading to typical optic nerve head damage and distinctive visual field defects. Although the pathogenesis of glaucoma is still largely unknown, it is hypothesized that RCGs become damaged through various insults/mechanisms, including ischemia, oxidative stress, excitotoxicity, defective axonal transport, trophic factor withdrawal, and neuroinflammation. In this review, we summarize the potential benefits of several natural compounds for RGCs neuroprotection.

Subtype-specific regeneration of retinal ganglion cells following axotomy: effects of osteopontin and mTOR signaling

In mammals, few retinal ganglion cells (RGCs) survive following axotomy, and even fewer regenerate axons. This could reflect differential extrinsic influences or the existence of subpopulations that vary in their responses to injury. We tested these alternatives by comparing responses of molecularly distinct subsets of mouse RGCs to axotomy. Survival rates varied dramatically among subtypes, with alpha-RGCs (αRGCs) surviving preferentially. Among survivors, αRGCs accounted for nearly all regeneration following downregulation of PTEN, which activates the mTOR pathway. αRGCs have uniquely high mTOR signaling levels among RGCs and also selectively express osteopontin (OPN) and receptors for the insulin-like growth factor 1 (IGF-1). Administration of OPN plus IGF-1 promotes regeneration as effectively as downregulation of PTEN; however, regeneration is still confined to αRGCs. Our results reveal dramatic subtype-specific differences in the ability of RGCs to survive and regenerate following injury, and they identify promising agents for promoting axonal regeneration.

Optic neuropathies: characteristic features and mechanisms of retinal ganglion cell loss

Optic neuropathy refers to dysfunction and/or degeneration of axons of the optic nerve with subsequent optic nerve atrophy. A common feature of different optic neuropathies is retinal ganglion cell (RGC) apoptosis and axonal damage. Glaucoma and optic neuritis are the two major degenerative causes of optic nerve damage. Here, we review the anatomy and pathology of the optic nerve, and etiological categories of optic neuropathies, and discuss rodent models that can mimic these conditions. Electrophysiology can reveal signature features of RGC damage using the pattern electroretinogram (PERG), scotopic threshold response (STR) and photopic negative response (PhNR). The amplitude of the visual evoked potential (VEP) also reflects RGC axonal damage. The neurotrophin-mediated survival pathways, as well as the extrinsic and intrinsic cell apoptotic pathways, play a critical role in the pathogenesis of RGC loss. Finally, promising neuroprotective approaches based on the molecular signaling are analyzed for the treatment of optic neuropathies.

Variable functional recovery and minor cell loss in the ganglion cell layer of the lizard Gallotia galloti after optic nerve axotomy

The lizard Gallotia galloti shows spontaneous and slow axon regrowth through a permissive glial scar after optic nerve axotomy. Although much of the expression pattern of glial, neuronal and extracellular matrix markers have been analyzed by our group, an estimation of the cell loss in the ganglion cell layer (GCL) and the degree of visual function recovery remained unresolved. Thus, we performed a series of tests indicative of effective visual function (pupillary light reflex, accommodation, visually elicited behavior) in 18 lizards at 3, 6, 9 and 12 months post-axotomy which were then processed for immunohistochemistry for the neuronal markers SMI-31 (neurofilaments), Tuj1 (beta-III tubulin) and SV2 (synaptic vesicles) at the last timepoint. Separately, cell loss in the GCL was estimated by comparative quantitation of DAPI(+) nuclei in control and 12 months experimental lizards. Additionally, 15 lizards were processed for electron microscopy to monitor relevant ultrastructural changes in the GCL, optic nerve and optic tract throughout regeneration. Hypertrophy of RGCs was persistent, morphology of the regenerated nerves varied from narrow to neuroma-like features and larger regenerated axons underwent remyelination by 9 months. The estimated cell loss in the GCL was 27% and two-third of the animals recovered the pupillary light reflex which involves the pretectum. Strikingly, visually elicited behavior involving the tectum was only restored in two specimens, presumably due to the higher complexity of this pathway. These preliminary results indicate that limited functional regeneration occurs spontaneously in the severely injured visual system of the lacertid G. galloti.

BDNF treatment and extended recovery from optic nerve trauma in the cat

PURPOSE

We examined the treatment period necessary to restore retinal and visual stability following trauma to the optic nerve.

METHODS

Cats received unilateral optic nerve crush and no treatment (NT), treatment of the injured eye with brain-derived neurotrophic factor (BDNF), or treatment of the injured eye combined with treatment of visual cortex for 2 or 4 weeks. After 1-, 2-, 4-, or 6-week survival periods, pattern electroretinograms (PERGs) were obtained and retinal ganglion cell (RGC) survival determined.

RESULTS

In the peripheral retina, RGC survival for NT, eye only, and eye + cortex animals was 55%, 78%, and 92%, respectively, at 1 week, and 31%, 60%, and 93%, respectively, at 2 weeks. PERGs showed a similar pattern of improvement. After 4 weeks, RGC survival was 7%, 29%, and 53% in each group, with PERGs in the dual-treated animals similar to the 1- to 2-week animals. For area centralis (AC), the NT, eye only, and eye + cortex animals showed 47%, 78%, and 82% survival, respectively, at 2 weeks, and 13%, 54%, and 81% survival, respectively, at 4 weeks. Removing the pumps at 2 weeks resulted in ganglion cell survival levels of 76% and 74% in the AC at 4 and 6 weeks postcrush, respectively. The PERGs from 2-week treated, but 4- and 6-week survival animals were comparable to those of the 2-week animals.

CONCLUSIONS

Treating the entire central visual pathway is important following optic nerve trauma. Long-term preservation of central vision may be achieved with as little as 2 weeks of treatment using this approach.

Time course modifications in organotypic culture of human neuroretina

The purpose of this study was to characterize organ culture of human neuroretina and to establish survival and early degeneration patterns of neural and glial cells. Sixteen neuroretina explants were prepared from 2 postmortem eyes of 2 individuals. Four explants were used as fresh retina controls, and 12 were evaluated at 3, 6, and 9 days of culture. Neuroretina explants (5 × 5 mm) were cultured in Transwell(®) dishes with the photoreceptor layer facing the supporting membrane. Culture medium (Neurobasal A-based) was maintained in contact with the membrane beneath the explant. Cryostat and ultrathin sections were prepared for immunohistochemistry and electron microscopy. Neuroretinal modifications were evaluated after toluidine blue staining and after immunostaining for neuronal and glial cell markers. Ultrastructural changes were analyzed by electron microscopy. From 0 to 9 days in culture, there was progressive retinal degeneration, including early pyknosis of photoreceptor nuclei, cellular vacuolization in the ganglion cell layer, decrease of both plexiform layer thicknesses, disruption and truncation of photoreceptor outer segments (OS), and marked reduction in the number of nuclei at both nuclear layers where the cells were less densely packed. At 3 days there was swelling of cone OS with impairment of pedicles, loss of axons and dendrites of horizontal and rod bipolar cells that stained for calbindin (CB) and protein kinase C (PKC-α), respectively. After 9 days, horizontal cells were pyknotic and without terminal tips. There were similar degenerative processes in the outer plexiform layer for rod bipolar cells and loss of axon terminal lateral varicosities in the inner plexiform layer. Glial fibrillary acidic protein (GFAP) staining did not reveal a dramatic increase of gliosis in Müller cells. However, some Müller cells were CB immunoreactive at 6 days of culture. Over 9 days of culture, human neuroretina explants underwent morphological changes in photoreceptors, particularly the OS and axon terminals, and in postsynaptic horizontal and bipolar cells. These early changes, not previously described in cultured human samples, reproduce some celullar modifications after retinal damage. Thus, this model may be suitable to evaluate therapeutic agents during retinal degeneration processes.

Endothelin B receptors contribute to retinal ganglion cell loss in a rat model of glaucoma

Glaucoma is an optic neuropathy, commonly associated with elevated intraocular pressure (IOP) characterized by optic nerve degeneration, cupping of the optic disc, and loss of retinal ganglion cells which could lead to loss of vision. Endothelin-1 (ET-1) is a 21-amino acid vasoactive peptide that plays a key role in the pathogenesis of glaucoma; however, the receptors mediating these effects have not been defined. In the current study, endothelin B (ET_B) receptor expression was assessed in vivo, in the Morrison's ocular hypertension model of glaucoma in rats. Elevation of IOP in Brown Norway rats produced increased expression of ET_B receptors in the retina, mainly in retinal ganglion cells (RGCs), nerve fiber layer (NFL), and also in the inner plexiform layer (IPL) and inner nuclear layer (INL). To determine the role of ET_B receptors in neurodegeneration, Wistar-Kyoto wild type (WT) and ET_B receptor-deficient (KO) rats were subjected to retrograde labeling with Fluoro-Gold (FG), following which IOP was elevated in one eye while the contralateral eye served as control. IOP elevation for 4 weeks in WT rats caused an appreciable loss of RGCs, which was significantly attenuated in KO rats. In addition, degenerative changes in the optic nerve were greatly reduced in KO rats compared to those in WT rats. Taken together, elevated intraocular pressure mediated increase in ET_B receptor expression and its activation may contribute to a decrease in RGC survival as seen in glaucoma. These findings raise the possibility of using endothelin receptor antagonists as neuroprotective agents for the treatment of glaucoma.

Morphometric analysis of optic nerves and retina from an end-stage retinitis pigmentosa patient with an implanted active epiretinal array

PURPOSE

To characterize optic nerve and retinal changes in a patient with end-stage retinitis pigmentosa (RP) with an implanted active epiretinal array.

METHODS

A 74-year-old man with end-stage X-linked RP underwent implantation of an epiretinal array over the macula in the right eye and subsequent stimulation until his death at 5 years and 3 months after implantation. The optic nerves from this study patient, as well as those from two age-matched normal patients and two age-matched RP patients, were morphometrically analyzed against two different sets of criteria and compared. The retina underlying the array in the study patient was also morphometrically analyzed and compared with corresponding regions of the retina in the age-matched RP patients.

RESULTS

Optic nerve total axon counts were significantly lower in the study patient and RP patients than in normal patients. However, there was no significant difference when comparing total axon counts from the optic nerve corresponding to the patient's implanted right eye versus the optic nerves from the RP patients (P = 0.59 and P = 0.61 using the two different criteria). Degenerated axon data quantified damage and did not show increased damage in the optic nerve quadrant that retinotopically corresponded to the site of epiretinal array implantation and stimulation. Except for the tack site, there was no significant difference when comparing the retina underlying the array and the corresponding perimacular regions of two RP patients.

CONCLUSIONS

Long-term implantation and electrical stimulation with an epiretinal array did not result in damage that could be appreciated in a morphometric analysis of the optic nerve and retina.

Susceptibility to N-methyl-D-aspartate toxicity in morphological and functional types of cat retinal ganglion cells

BACKGROUND

To examine whether different types of retinal ganglion cells (RGCs) in the cat retina have different survival rates when exposed to N-methyl-D-aspartate (NMDA).

METHODS

NMDA injury was induced by intravitreal administration of NMDA at final concentrations of 0.2, 0.4, 0.6, and 0.8 mM. The total number of surviving RGCs and their distribution were counted by retrograde labeling with a fluorescent dye. Measurements of the proportions of the main RGC types (alpha, beta, and neither alpha nor beta cells) were obtained by using intracellular injections of Lucifer yellow.

RESULTS

The mean percentage of surviving RGCs in the NMDA-injected retina was reduced to 59.4% (0.2 mM NMDA), 35.8% (0.4 mM), 10.8% (0.6 mM), and 14.1% (0.8 mM). At 0.2 mM, the survival rate of alpha cells was reduced to 56%, but that of beta cells remained at 81%. At 0.8 mM, the survival rate of alpha cells was 19%, while beta cells rapidly decreased to 9.9%. No difference was detected in NMDA vulnerability between ON- and OFF-center RGCs.

CONCLUSIONS

Different RGC types display different susceptibilities to NMDA injury. A specific examination of the functions of different types of RGCs would be helpful in detecting retinal excitotoxicity such as in chronic retinal ischemia.

Mitogen-activated protein kinase-signaling regulates the ability of Müller glia to proliferate and protect retinal neurons against excitotoxicity

The purpose of this study was to investigate whether insulin, fibroblast growth factor (FGF), and mitogen-activated protein kinase (MAPK) pathways protect retinal neurons against excitotoxicity and regulate the proliferation of Müller glia. We found that intraocular injections of insulin or FGF2 had variable effects upon the phosphorylation of ERK1/2, p38 MAPK, and CREB, and the expression of immediate early genes, cFos and Egr1. Accumulations of pERK1/2, p38 MAPK, pCREB, cFos and Egr1 in response to insulin or FGF2 were confined to Müller glia, whereas retinal neurons did not seem to respond to growth factors. Unlike FGF2, insulin stimulated microglia-like cells to upregulate the intermediate filament transitin and lysosomal membrane glycoprotein (LMG). With microglia-like cells and Müller glia stimulated by insulin or FGF2 there were profound effects upon numbers of dying neurons in response to excitotoxic damage. Although FGF2 significantly reduced numbers of dying neurons, insulin significantly increased numbers of dying neurons. In addition to neuroprotective affects, FGF2 also "primed" the Müller glia to proliferate following retinal damage, whereas insulin had no effect upon glial proliferation. Further, we found that FGF receptor isoform 1 (FGFR1) and FGFR3 were prominently expressed in the retina, whereas the insulin receptor and FGFR2 are not expressed, or are expressed at very low levels. We conclude that MAPK-signaling through FGF receptors stimulates Müller glia to become more neuroprotective and progenitor-like, whereas insulin acting on Müller and microglia-like cells through unidentified receptors had the opposite effect.

Neuroprotective effect of transretinal electrical stimulation on neurons in the inner nuclear layer of the degenerated retina

Electrical stimulation has been shown to have neuroprotective effects on ganglion cells and photoreceptors in axotomized and dystrophic retinas from Royal College of Surgeons (RCS) rats. This study determined whether electrical stimulation also has a neuroprotective effect on cells in the inner nuclear layer (INL) of retinas. We cultivated retinas from adult RCS rats on microelectrode arrays and stimulated them continuously with 20 Hz for up to 5 days. Afterwards, we subjected them to quantitative immunohistochemical analysis. Using TUNEL assay we found that transretinal electrical stimulation (TRES) with charge densities within the range of 100-500 microC/cm2 reduced apoptosis of neurons in the INL of degenerated retinas from RCS -/- rats by 20% after 1 day of continuous stimulation. Antibody staining (OX-42, ED1) revealed a reduced activation of migroglial cells in RCS -/- and congenic control (RCS +/+) rat retinas by up to 50% after 1 day of stimulation. The effect of electrical stimulation on apoptosis and reduced activation of microglial cells was closely correlated with the strength and duration of the stimulation. The neuroprotective effect of TRES on neuronal cells in the INL of degenerated RCS rat retinas supports the idea that electrical stimulation may be a therapeutic option to delay the progression of retinal degeneration in patients suffering from retinitis pigmentosa.

Effect of CNTF on retinal ganglion cell survival in experimental glaucoma

PURPOSE

To assess the neuroprotective effect of virally mediated overexpression of ciliary-derived neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) in experimental rat glaucoma.

METHODS

Laser-induced glaucoma was produced in one eye of 224 Wistar rats after injection of adenoassociated viral vectors (type 2) containing either CNTF, BDNF, or both, with saline-injected eyes and noninjected glaucomatous eyes serving as the control. IOP was measured with a hand-held tonometer, and semiautomated optic nerve axon counts were performed by masked observers. IOP exposure over time was adjusted in multivariate regression analysis to calculate the effect of CNTF and BDNF.

RESULTS

By multivariate regression, CNTF had a significant protective effect, with 15% less RGC axon death (P < 0.01). Both combined CNTF-BDNF and BDNF overexpression alone had no statistically significant improvement in RGC axon survival. By Western blot, there was a quantitative increase in CNTF and BDNF expression in retinas exposed to single viral vectors carrying each gene, but no increase with sequential injection of both vectors.

CONCLUSIONS

These data confirm that CNTF can exert a protective effect in experimental glaucoma. The reason for the lack of observed effect in the BDNF overexpression groups is unclear, but it may be a function of the level of neurotrophin expression achieved.

The neuropeptide NAP provides neuroprotection against retinal ganglion cell damage after retinal ischemia and optic nerve crush

BACKGROUND

NAP, an 8-amino acid peptide (NAPVSIPQ=Asn-Ala-Pro-Val-Ser-Ile-Pro-Gln) derived from activity-dependent neuroprotective protein (ADNP), plays an important role in neuronal differentiation and the survival of neurons in different pathological situations. We already discovered that NAP increases the survival of retinal ganglion cells (RGC) in vitro, and supports neurite outgrowth in retinal explants at femtomolar concentrations. The aim of this study was to investigate the effects of NAP on RGC survival after transient retinal ischemia and optic nerve crush.

METHODS

RGC of male Wistar rats were labelled retrogradely with 6 l FluoroGold injected stereotactically into both superior colliculi. Seven days later, retinal ischemia was induced by elevating the intraocular pressure to 120 mm Hg for 60 minutes or by crushing one optic nerve for 10 s after a partial orbitotomy. NAP was either injected intraperitoneally in the concentration of 100 microg/kg [corrected] 1 day before, directly after, and on the first and the second days after damage, or intravitreally (0.05 or 0.5 microg/eye) [corrected] directly after the optic nerve crush. Controls received the same concentrations of a control peptide. Densities of surviving RGC and activated microglial cells (AMC) were quantified in a masked fashion 10 days after damage by counting FluoroGold-labelled cells.

RESULTS

After retinal ischemia, intraperitoneal injections of NAP increased the number of surviving RGC by 40% (p < 0.005) compared to the control group. After optic nerve crush, NAP raised the number of surviving RGC by 31% (p = 0.07) when injected intraperitoneally and by 54% (p < 0.05) when administered intravitreally.

CONCLUSIONS

NAP acts neuroprotectively in vivo after retinal ischemia and optic nerve crush, and may have potential in treating optic nerve diseases.

Differential effects of two ROCK inhibitors, Fasudil and Y-27632, on optic nerve regeneration in adult cats

A ROCK inhibitor Fasudil is widely administered to relieve vasospasm in patients after subarachnoid hemorrhage in Japan. We investigated the difference of Fasudil and Y-27632, a common ROCK inhibitor, on neurite regeneration in culture and axonal regeneration after injuring the optic nerve (OpN) in cats. The optimal dose of Y-27632, determined by counting the number and length of neurites in retinal explants, was found to be 100 microM: the only effect of Fasudil was to promote extension of glial processes. We next examined the effects of Fasudil (10 microM-100 microM) and Y-27632 (10 microM-300 microM) on axonal regeneration in the crushed OpN model in vivo. Immediately after crushing the left OpN, Fasudil or Y-27632 was injected into the vitreous and the crushed site. Injection of 10 microM and 100 microM Y-27632 induced extension of the optic axons beyond the crush site, with the latter dosage giving stronger regeneration. Very few axons passed beyond the crush site in the optic nerve with phosphate-buffered saline injection, and no axons elongated in the OpN with Fasudil injection.

Survival and axonal regeneration of off-center retinal ganglion cells of adult cats are promoted with an anti-glaucoma drug, nipradilol, but not BDNF and CNTF

OFF-center retinal ganglion cells (RGCs) occupy a smaller proportion than ON RGCs when RGCs regenerate axons into a transplanted peripheral nerve. We examined whether the regeneration ability of OFF RGCs in adult cats was promoted when the numbers of regenerating RGCs were increased with brain-derived neurotrophic factor (BDNF)+ciliary neurotrophic factor (CNTF)+forskolin (BCF) or 3,4-dihydro-8-(2-hydroxy-3-isopropylamino)-propoxy-3-nitroxy-2H-1-benzopyran (nipradilol), an anti-glaucoma drug. ON or OFF RGCs were morphologically determined on the basis of their dendritic ramification in the inner plexiform layer using computational analysis. In the normal intact retina the ratio of ON and OFF RGCs (ON/OFF ratio) was 1.25 (55%/44%); whereas, it was 2.61 in regenerating RGCs with saline injection (control) 6 weeks after peripheral nerve transplantation. Estimated numbers of regenerating ON and OFF RGCs were 2149 and 895, respectively. An injection of BCF increased only numbers of ON RGCs into 5766 (2.7-fold to control) but not that of OFF RGCs, n=858. Nipradilol increased both estimated numbers of ON (11,518, 5.4-fold to control) and OFF RGCs (7330, 8.2-fold to control). In the retinas with optic nerve (OpN) transection and intravitreal saline-, BCF- or nipradilol-injection, numbers of ON and OFF RGCs surviving axotomy showed similar trend to that in regenerating RGCs. Thus, nipradilol promoted the survival and regeneration abilities of both of ON and OFF RGCs whereas BCF only did the abilities of ON RGCs. The distribution of tropo-myosin-related kinase B, BDNF receptor, was sparser in the outer two thirds of inner plexiform layer. The lower surviving ability of OFF-RGCs may be attributed in part to the distribution.

Neurotrophic factors and neural prostheses: potential clinical applications based upon findings in the auditory system

Spiral ganglion neurons (SGNs) are the target cells of the cochlear implant, a neural prosthesis designed to provide important auditory cues to severely or profoundly deaf patients. The ongoing degeneration of SGNs that occurs following a sensorineural hearing loss is, therefore, considered a limiting factor in cochlear implant efficacy. We review neurobiological techniques aimed at preventing SGN degeneration using exogenous delivery of neurotrophic factors. Application of these proteins prevents SGN degeneration and can enhance neurite outgrowth. Furthermore, chronic electrical stimulation of SGNs increases neurotrophic factor-induced survival and is correlated with functional benefits. The application of neurotrophic factors has the potential to enhance the benefits that patients can derive from cochlear implants; moreover, these techniques may be relevant for use with neural prostheses in other neurological conditions.

Adult retinal neuronal cell culture

Despite a relatively long history, general knowledge is not widespread that adult neurons can be maintained in cell culture for fairly extended periods of time. Within the central nervous system, this capacity seems to be particularly well developed in the retina, although it is still not clear whether this property is due to physical reasons (spatial configuration, simple connections) or to more fundamental differences (molecular composition, physiological function). Irrespective of the reasons, in vitro model systems are useful for investigating physiological and pathological processes occurring in mature retina. The authors argue that the numerous molecular changes undergone during maturation (modifications in ion channels and receptors, apoptotic pathways and growth factor effects) should be taken into account when using in vitro approaches to study processes involved in photoreceptor and ganglion cell degeneration, and hence that more classical methods relying on embryonic or newborn tissue should be interpreted with caution. A number of examples are given where the use of adult retinal neuronal culture may be especially informative: neurite regeneration, neuroprotection assays and pathogenic mechanisms; and areas of further research that should be explored: cell transplantation.

Gene therapy and transplantation in CNS repair: The visual system

Normal visual function in humans is compromised by a range of inherited and acquired degenerative conditions, many of which affect photoreceptors and/or retinal pigment epithelium. As a consequence the majority of experimental gene- and cell-based therapies are aimed at rescuing or replacing these cells. We provide a brief overview of these studies, but the major focus of this review is on the inner retina, in particular how gene therapy and transplantation can improve the viability and regenerative capacity of retinal ganglion cells (RGCs). Such studies are relevant to the development of new treatments for ocular conditions that cause RGC loss or dysfunction, for example glaucoma, diabetes, ischaemia, and various inflammatory and neurodegenerative diseases. However, RGCs and associated central visual pathways also serve as an excellent experimental model of the adult central nervous system (CNS) in which it is possible to study the molecular and cellular mechanisms associated with neuroprotection and axonal regeneration after neurotrauma. In this review we present the current state of knowledge pertaining to RGC responses to injury, neurotrophic and gene therapy strategies aimed at promoting RGC survival, and how best to promote the regeneration of RGC axons after optic nerve or optic tract injury. We also describe transplantation methods being used in attempts to replace lost RGCs or encourage the regrowth of RGC axons back into visual centres in the brain via peripheral nerve bridges. Cooperative approaches including novel combinations of transplantation, gene therapy and pharmacotherapy are discussed. Finally, we consider a number of caveats and future directions, such as problems associated with compensatory sprouting and the reformation of visuotopic maps, the need to develop efficient, regulatable viral vectors, and the need to develop different but sequential strategies that target the cell body and/or the growth cone at appropriate times during the repair process.

Application of encapsulated cell technology for retinal degenerative diseases

Ophthalmic disorders represent a rapidly growing disease area that is associated with the ageing population. Their sight is threatened by age-related macular degeneration, diabetic retinopathy, glaucoma and/or retinitis pigmentosa (RP). Few effective treatments for these disorders are available at present, in part due to lack of effective delivery of therapeutic molecules to the retina. Encapsulated cell technology (ECT) allows the controlled, continuous and long-term administration of protein drugs in the eye, where therapeutic agents are needed, and does not subject the host to the systemic exposure. Furthermore, the implants can be retrieved, providing an added level of safety. Ciliary neurotrophic factor (CNTF) has been shown to protect the retina from degeneration in 13 animal models, and ECT-based delivery of CNTF protected photoreceptors in the rcd1 dog model of RP.

CNTF gene transfer protects ganglion cells in rat retinae undergoing focal injury and branch vessel occlusion

Ciliary neurotrophic factor (CNTF) has been shown to protect ganglion cells in a variety of acute ischaemia models. Here we assess the efficacy of local CNTF gene transfer in protecting retinal ganglion cells when there is focal ischaemia combined with interruption of axoplasmic flow. This dual injury may be more representative of the pathological mechanisms operating in acute retinal diseases, such as vascular events acting at the optic nerve head. Fourteen rats received an intravitreal injection of an adeno-associated viral (AAV) vector expressing a secretable form of CNTF into the right eye and a control vector into the left eye. Three weeks later, each rat underwent a symmetrical small vertical 2mm standardised retinal crush injury approximately 2mm temporal to the optic disc. The injury also occluded the temporal retinal arteriole so that the axon crush was combined with an acute retinal infarction visible on fundoscopy. Changes in the damaged sector were compared histologically four weeks after injury and ganglion cell survival was estimated by comparing cell counts on retinal flat-mounts immunostained with RT-97 antibody. This mode of injury led to a profound loss of both the inner nuclear and ganglion cell layers, but was limited to the lesioned sector. In AAV.CNTF-treated eyes approximately 12% of ganglion cells survived compared with approximately 2% in control eyes (p=0.01). The scotopic electroretinogram (ERG), however, was reduced to about 50% in AAV.CNTF-treated eyes, both before and after injury. We therefore show that CNTF gene transfer confers neuroprotection to ganglion cells undergoing an acute ischaemic injury combined with interruption of axoplasmic flow. This approach may be relevant to optic nerve trauma and a variety of retinal vascular diseases that lead to swelling of the optic nerve head, provided CNTF can be delivered in a way that does not significantly suppress retinal function.

CNTF induces dose-dependent alterations in retinal morphology in normal and rcd-1 canine retina

Ciliary neurotrophic factor (CNTF) provides morphologic preservation of rods in several animal models of retinitis pigmentosa (RP). However, CNTF may alter photoreceptor morphology and rod photoreceptor differentiation in vitro, as well as affecting normal retinal electrophysiology. In addition, the capacity of CNTF to support other cell types affected secondarily in RP (cones and ganglion cells) is unclear. The purposes of this study were to examine the effects of CNTF upon a canine model of RP, the rod-cone degeneration (rcd-1) dog. Archival tissue from a previous study assessing the capacity of CNTF to rescue photoreceptors in rcd-1 dogs was used. One eye was treated for 7 weeks before being explanted. The contralateral eye was untreated. A total of 23 rcd-1 dogs and seven control dogs (four untreated and three CNTF-treated) were used. Morphometric data describing outer and inner nuclear layer thickness, inner retinal thickness, cones and ganglion cells were collected at nine evenly spaced points along each retina and analysed using a mixed effects model. Immunohistochemistry was performed on a subset of 11 dogs for expression of rhodopsin, human cone arrestin (hCAR) and recoverin. CNTF protected the outer nuclear layer and increased inner retinal thickness in a dose-dependent manner (both were maximal at CNTF doses of 1-6 ng day-1). Significant cone loss or reduction of inner nuclear layer width in rcd-1 did not occur in this model, therefore we were unable to assess the protective effect of CNTF upon these parameters. CNTF did not afford significant ganglion cell protection. CNTF induced morphologic changes in rods and ganglion cells, as well as reducing expression of hCAR and rhodopsin, but not recoverin. The dose of CNTF which provided optimal outer nuclear layer protection also resulted in several other effects, including altered ganglion cell morphology, increased thickness of the entire retina, and reduced expression of some phototransduction proteins. These changes were more marked in rcd-1 retinas than in wild-type retinas. This implies that the consequences of CNTF treatment may be substantially influenced by the cellular context into which it is introduced.

Light delays synaptic deafferentation and potentiates the survival of axotomized retinal ganglion cells

Knowledge of the cellular mechanism underlying the therapeutic effect of stimulation and the optimal doses of such stimulation to maximize neuronal recovery is essential to guide clinical practice in neural rehabilitation. Using hamsters, we transected the optic nerve to demonstrate how light stimulation affects neuronal recovery. The c-fos protein was used as a neuronal connectivity marker. Here we show that: (a) in addition to cell death, a population of cells undergoes synaptic deafferentation and (b) light stimulation delays cell death and deafferentation. Among the three rearing conditions studied (6:18LD, 12:12LD, and 18:6LD), the 12:12LD condition appears to be the one achieving the optimal therapeutic effect. This study provides a solid base in the understanding of the neuroanatomical changes after traumatic brain injury and the need to establish an optimal level and timing for the environmental stimulation.

Axonal regeneration of cat retinal ganglion cells is promoted by nipradilol, an anti-glaucoma drug

Neurons in the CNS can regenerate their axons in an environment of the peripheral nervous system, but this ability is limited. Here we show that an anti-glaucoma drug, nipradilol, at low concentration led to a four-fold increase in the number of cat retinal ganglion cells regenerating their axons into a transplanted peripheral nerve 4 and 6 weeks after axotomy. Nipradilol also increased the number of three main regenerating retinal ganglion cell types (alpha, beta, not alpha/beta), and enhanced the rate of axonal regeneration of these retinal ganglion cells. Nipradilol is a donor of nitric oxide and an antagonist of alpha-1, beta-1 and -2 adrenoreceptors, and we therefore examined whether one of these pharmacological effects might be more important in promoting axon regeneration. A nitric oxide donor increased the number of regenerating retinal ganglion cells, but not the rate of axonal regeneration. Denitro-nipradilol (nitric oxide-deprived nipradilol) or a nitric oxide scavenger injected before nipradilol increased the number of regenerating retinal ganglion cells but did not promote regeneration rate. Blockade of individual alpha- and beta-adrenoreceptors did not increase the number of regenerating retinal ganglion cells or the rate of regeneration. From these results, it is suggested that nitric oxide plays a crucial role in mediating the effects of nipradilol on axon regeneration and neuroprotection, and the metabolite of nipradilol supports the effects.

Selective upregulation of RB3/stathmin4 by ciliary neurotrophic factor following optic nerve axotomy

In this study, we examined the cellular responses of stathmin-related proteins in the rat retina following optic nerve (ON) axotomy. To examine the distribution of stathmin-related gene products, we performed semi-quantitative reverse transcription polymerase chain reaction (RT-PCR), in situ hybridization (ISH) and immunohistochemical analyses. Retrograde labeling using a fluorescein tracer, fluorogold (FG), was used for the identification of retinal ganglion cells (RGCs). RT-PCR and ISH analyses indicated that the expression of RB3 was specifically increased in the ganglion cell layer (GCL) comparing to other members of stathmin-related gene family examined 3 days following the ON axotomy. When brain-derived neurotrophic factor was administrated intravitreously, the induction of RB3 mRNA sustained up to 7 days after axotomy, although the peak induction level was unchanged. In contrast, ciliary neurotrophic factor (CNTF) administration increased the peak level of RB3 mRNA induction significantly at 3 days after axotomy. Immunohistochemistry in combination with the retrograde labeling of axotomized cells by FG revealed that RB3 was increased following axotomy in FG-labeled RGCs. These data suggest that RB3 is the unique response protein in the stathmin-related proteins following ON axotomy and the induced RB3 may play a critical role in the CNTF-induced response on the axotomized RGCs, e.g. axonal regeneration and/or neuroprotection.

JNK inhibitory kinase is up-regulated in retinal ganglion cells after axotomy and enhances BimEL expression level in neuronal cells

Optic nerve transection results in retinal ganglion cell (RGC) death in adult mammals, after the alteration of gene expression of RGCs. To elucidate the molecular mechanism by which axotomy induces RGC death, we isolated the molecules up-regulated after optic nerve transection. One of these, axotomy-related [corrected] gene (ARG)357, an 898-amino-acid [corrected] protein containing a complete serine-threonine kinase domain, was isolated from a subtraction library of the rat retina. The sequence showed that this gene was a rat homolog of human c-Jun N-terminal kinase (JNK) inhibitory kinase and so belonged to the germinal center kinase-VIII subfamily of Sterile20s protein kinase. We designated ARG357 as rat JNK inhibitory kinase (JIK). Rat JIK was expressed ubiquitously in various tissues and was highly expressed in the retina, with selective expression in RGCs. After axotomy, BimEL and Hrk, which are BH3-only proteins, and rat JIK were up-regulated in RGCs. Overexpression of rat JIK in neuronal cells up-regulated the expression of BimEL, but not that of Hrk. These results indicate that JIK may contribute to axotomy-induced RGC death by up-regulating the expression of BH3-only protein.

Intravitreal macrophage activation enables cat retinal ganglion cells to regenerate injured axons into the mature optic nerve

In mature mammals, retinal ganglion cells (RGCs) are generally unable to regenerate injured axons into the optic nerve. Here, we report that an intravitreal injection of either of two macrophage activators, oxidized galectin-1 or zymosan, strongly enhanced the regeneration of transected RGC axons beyond an optic nerve crush site in adult cats. Using WGA-HRP as an anterograde tracer, we found that injection of either macrophage activator caused many axons to grow into the distal optic nerve when evaluated 14 days later, with the strongest effects seen after injecting 100 ng of galectin-1. Elongation continued for at least another 2 weeks. Control eyes injected with saline contained very few labeled axons extending across the crush site. Elevation of intracellular cAMP levels using forskolin also enhanced regeneration beyond the crush site to some extent, but this treatment did not augment the effect of galectin-1 any further. These results indicate that RGCs of adult cats are capable of reverting to an active growth state and at least partially overcoming an inhibitory CNS environment as a result of intravitreal macrophage activation.