Microglia-targeted pharmacotherapy in retinal neurodegenerative diseases

Microglial cells, members of the monocytic lineage, represent the resident immunocompetent cells of the central nervous system including the retina with its peculiarities like a double blood retinal barrier. Microglial cells invade the retina in response to naturally occurring neuronal death during embryonic development and remodelling. Resident microglial cells are extremely sensitive to changes in their microenvironment arising from either traumatic or chronic neurodegeneration, inproper wiring, hereditary diseases or infection and become rapidly activated. In their activated state, the cells undergo drastic morphological changes, upregulate a variety of receptors and secrete soluble factors, which contribute to recognition and phagocytotic cleareance of dying or malfunctioning neurons. In this review, we aim to summarise the current knowledge of microglial involvement in experimentally induced or naturally occurring retinal neurodegenerations with emphasising on mechanisms of microglia activation. Expanding on the mechanisms, we shall discuss on approaches to pharmacologically interfere with the microglial activation and neurophagy. The protagonistic role of these cells in the outcome of certain diseases may help designing microglial targeted treatments with potential benefit for neuronal survival and regeneration in clinically relevant conditions.

Role of a neuronal small non-messenger RNA: behavioural alterations in BC1 RNA-deleted mice

BC1 RNA is a small non-messenger RNA common in dendritic microdomains of neurons in rodents. In order to investigate its possible role in learning and behaviour, we compared controls and knockout mice from three independent founder lines established from separate embryonic stem cells. Mutant mice were healthy with normal brain morphology and appeared to have no neurological deficits. A series of tests for exploration and spatial memory was carried out in three different laboratories. The tests were chosen as to ensure that different aspects of spatial memory and exploration could be separated and that possible effects of confounding variables could be minimised. Exploration was studied in a barrier test, in an open-field test, and in an elevated plus-maze test. Spatial memory was investigated in a Barnes maze and in a Morris water maze (memory for a single location), in a multiple T-maze and in a complex alley maze (route learning), and in a radial maze (working memory). In addition to these laboratory tasks, exploratory behaviour and spatial memory were assessed under semi-naturalistic conditions in a large outdoor pen. The combined results indicate that BC1 RNA-deficient animals show behavioural changes best interpreted in terms of reduced exploration and increased anxiety. In contrast, spatial memory was not affected. In the outdoor pen, the survival rates of BC1-depleted mice were lower than in controls. Thus, we conclude that the neuron-specific non-messenger BC1 RNA contributes to the aptive modulation of behaviour.

[Neuroprotection and regeneration after traumatic lesion of the optic nerve]

BACKGROUND

After a traumatic lesion of the optic nerve, retinal ganglion cells (RGC) undergo massive degeneration by apoptosis, which leads to loss of vision in the affected eye. Like other neurones in the central nervous system, RGC are not able to regenerate their damaged axons spontaneously. We used special surgical methods and pharmacological measures to achieve enhanced survival and regeneration of damaged RGC.

MATERIALS AND METHODS

Studies were performed using the model of RGC degeneration induced by severing the optic nerve of adult rats. RGC were loaded with a fluorescent dye, and several drugs were applied intravitreally. The effects were evaluated after two weeks by counting the surviving RGC. For regeneration studies, an autologous peripheral nerve graft was sutured to the stump of the cut optic nerve, or the ends of the cut optic nerve were re-sutured. Recovery of RGC function was assessed by VEP measurements.

RESULTS

The number of RGC surviving an axotomy increased significantly after intravitreal injections of aurintricarboxylic acid, cortisol, a caspase inhibitor, brimonidine or microglia-targeted substances. Regeneration of cut axons was enhanced by aurintricarboxylic acid or cortisol. In addition, considerable neuroprotective and regenerative effects including partial restoration of VEP were induced by lens injury, which results in a gradual release of crystallins into the vitreous, or by intravitreal injection of purified crystallins.

CONCLUSION

The loss of vision after an optic nerve trauma can be reduced in this animal model by suitable neuroprotective measures, which raises hope for the treatment of patients.

Presurgical and postsurgical ultrasound assessment of lacrimal drainage dysfunction

PURPOSE

In addition to the obligatory clinical tests, imaging of the lacrimal drainage system (LDS) is useful in its clinical evaluation. The purpose of this study was to examine the usability and reliability of ultrasonography in the evaluation of the lacrimal drainage system.

DESIGN

Observational cohort study.

METHODS

A prospective study was conducted at a single institution. We performed ultrasound examinations on 17 patients with epiphora before and after surgery, and on 17 asymptomatic volunteers, to visualize and evaluate the anatomic and functional condition or pathologic abnormalities of the LDS.

RESULTS

Echographic evaluation of the LDS was possible in all individuals. Pathologic abnormalities (canaliculitis, diverticulitis, concretion, or dilation of the lacrimal sac, and reduced functionality of the orbicular muscle and/or lacrimal sac pump) could be well demonstrated. In the postsurgical course, functional patency of the dacryocystorhinostomy opening could be verified in all cases.

CONCLUSIONS

Sonography of the LDS appears to represent a reliable diagnostic technique supplementary to clinical tests in the presurgical and postsurgical examination of patients with epiphora. Pathologic abnormalities that may not be apparent in routine x-ray dacryocystography can be demonstrated with ultrasound techniques. Patients also benefit from the avoidance of exposure to ionizing radiation. However, ultrasound is not suitable for imaging the lower part of the lacrimal sac and the lacrimal duct because of the presence of overlying bony structures.

Decorin deficiency leads to impaired angiogenesis in injured mouse cornea

Small leucine-rich proteoglycans play important roles in the organization of the extracellular matrix as well as for the regulation of cell behavior; two biological processes that are essential for angiogenesis. We investigated consequences of the targeted ablation of decorin (DCN), biglycan (BGN) and fibromodulin (FMOD) genes on inflammation-induced angiogenesis in the cornea. In wild-type mice, DCN was localized exclusively to the corneal stroma, while FMOD and BGN were more prominently expressed in epithelial cells. Endothelial cells from limbus blood vessels expressed BGN and FMOD, but no DCN. However, after induction of angiogenesis by chemical cauterization, DCN was expressed in the newly formed capillaries, together with BGN and FMOD. Notably, in DCN-deficient mice, the growth of vessels was significantly diminished, whereas it did not significantly change in FMOD- or BGN-deficient animals. Moreover, blood vessels of DCN-deficient mice exhibited a similar expression level of BGN as control mice, while FMOD was increased on day 3 after injury. These results indicate that DCN, in addition to its effects on fibrillogenesis, plays a regulatory role in angiogenesis and that FMOD in endothelial cells may be able to partially substitute for DCN.

Neuronal MAP2 mRNA: Species-dependent Differential Dendritic Targeting Competence

Providing the basis for local protein synthesis in dendritic microdomains, RNA transport in dendrites is thought to be underlying long-term neuronal plasticity. Dendritic RNA targeting mechanisms can therefore be expected to confer selective advantages in the evolution of complex neural systems. The question thus arises as to when and how dendritically targeted transcripts first acquired their targeting competence. To address this question, the dendritic targeting competence of MAP2 transcripts was examined in chicken, mouse and rat. In one approach, we established the somato-dendritic distribution of MAP2 transcripts in vivo. We found that in contrast to rodent MAP2 mRNAs, which are highly enriched in dendritic regions of the retina, chicken MAP2 transcripts are virtually absent from such areas and are rather confined to neuronal somata. In an independent line of investigation, we determined that a dendritic targeting element (DTE) corresponding to the mammalian MAP2 DTE is not contained in the 3' untranslated region (UTR) of avian MAP2 mRNA. The combined results indicate that in contrast to mammalian MAP2 transcripts, avian MAP2 mRNA is lacking dendritic targeting competence. The data thus suggest that the acquisition of such competence has likely been a relatively recent event in evolution.

Neuro-glial interactions in the adult rat retina after reaxotomy of ganglion cells: examination of neuron survival and phagocytic microglia using fluorescent tracers

Retinal ganglion cells (RGCs) regenerating through peripheral nerve grafts show enhanced survival after further axonal injury for at least 4 weeks [Restor. Neurol. Neurosci. 21 (2003) 11]. Here, we examined the survival of the neurons and their microglial phagocytosis in dependence of the site of reaxotomy. Therefore, the optic nerve in adult rats was transected at different distances from the eye cup and replaced with an autologous piece of sciatic nerve. After 14 days of axonal growth, the regenerated neurites were reaxotomized either within the remaining optic stump or within the graft and their cell bodies were retrogradely labeled. Reaxotomy of regenerated ganglion cells within the remaining optic nerve resulted in reduced (but not significant) ganglion cell survival and significant microglial phagocytosis in contrast to reaxotomy within the peripheral nerve graft. Furthermore, phagocytosis-dependent labeling using two different fluorescent tracers revealed that the same microglial cell can phagocytose further dying ganglion cells within 14 days after the first activation. The results suggest that the intrasciatic segments of axons receive some trophic support that is retrogradely transported and required to limit the microglial activation. The microglial capability to phagocytose dying neurons several fold emphasizes their function in permanent scavenging within the retina.

Correlation between retinal ganglion cell death and chronically developing inherited glaucoma in a new rat mutant

Glaucoma is a progressive optic neuropathy with characteristic optic disc changes, retinal ganglion cell loss and progressive visual field defects. Elevated intraocular pressure is considered to be a major risk factor in glaucomatous neuropathy. This study aimed to characterize and document a new chronic glaucoma model in the rat with respect to the effect of elevated intraocular pressure on overall retinal dysfunction and retinal ganglion cell loss, and to elucidate the possible mechanisms underlying this cell loss. Intraocular pressure (IOP) was measured in rats using a Tonopen. RGCs were retrogradely labeled with the fluorescent dye, 4-[didecylaminostyryl]-N-methyl-pyridinium-iodide (4-Di-10 ASP) and quantified on retinal flat mounts using fluorescence microscopy. The optic nerve head was examined fundoscopically. Changes in the histological appearance of the whole eyes was studied in paraffin sections, and immunohistochemistry was carried out on cryostat sections. The levels of mRNA for several genes were compared between control and glaucomatous retinae using semi-quantitative RT-PCR. Mutant animals are affected with either a unilateral or bilateral enlargement of the globes having an IOP that ranged from 25 to 45 mmHg, as compared to control values of 12-16 mmHg. The IOP of glaucomatous eyes increased significantly with age to attain a value of 35+/-7.3 at 1.5 years. Concomitant with the rise in IOP, the number of labeled RGCs continued to decrease in number with age. A total of 1887+/-117RGC mm(-2) could be labeled in wild-type control and juvenile mutant pre-glaucomatous retinas, whereas this number dropped to 92+/-26RGC mm(-2) at 1.5 years. Ophthalmoscopy revealed atrophied optic nerve heads in the affected eyes. The pars plicata and the pars plana of the ciliary body of glaucomatous eyes were hypertrophied and elongated, respectively. The anterior chamber was narrow and the irido-corneal angle open in glaucoma eyes. The mRNA of glial-fibrillary-acidic protein, endothelin-1, STAT-3 and STAT-6 increased in the retinas correlating with the severity and duration of the disease. Changes in the expression of GFAP and endothelin-1 could be confirmed using immunohistochemistry. This model may help to address several fundamental issues in the pathogenesis of glaucoma and aid in the development of neuroprotective strategies.

Potential role of Pax-2 in retinal axon navigation through the chick optic nerve stalk and optic chiasm

The degree of fiber decussation at the optic chiasm differs between species, ranging from complete crossing in lower vertebrates to highly complex patterns of intermingling of the fibers from the two eyes seen in mammals and birds. Understanding the genetic control of fiber guidance through the chiasm is therefore important to unravel the developmental mechanisms within the visual system. Here we first report on early stages of chiasm formation, with pioneering axons from the left eye consistently arriving earlier than their counterparts from the right eye. This initial left-right asymmetry is transient and no functional significance is assigned to it yet. Secondly, we examined formation of the chiasm in relation with the expression of the transcription factor Pax-2 along the ventral eye cup and optic nerve stalk. Finally, in order to examine causal involvement of Pax-2 in chiasm formation, the gene was overexpressed along the neuraxis and in the eye cup at embryonic stages preceding the exit of axons from the eye, and hence arrival of axons at the chiasm. When studied with neuroanatomical tracing, Pax-2 overexpression resulted in visibly anomalous decussation of axons at the chiasm. A likely consequence of this perturbation was erroneous arrival of axons at the tectum, as observed by anterograde staining from the retina. These data suggest that balanced expression of Pax-2 results in the correct formation of the chick chiasm at early stages by imposing accurate pathfinding within the optic stalk and the midline.

Distribution of scotoma pattern related to chiasmal lesions with special reference to anterior junction syndrome

PURPOSE

To evaluate pathogenetic mechanisms and frequency distribution of visual field defects (VFDs) in patients with chiasmal lesions. Secondly, to reconsider the existence of "Wilbrand's knee" as far as referable to the anterior junction syndrome.

METHODS

Consecutive visual field records related to chiasmal lesions were retrieved from the Tuebingen Perimetric Database. In all cases, at least one eye was examined with the Tuebingen Automated Perimeter using a standardized grid of 191 static targets within the central 30 degrees visual field, and a threshold-related, slightly supraliminal strategy. VFDs were classified according to standard neuro-ophthalmological categories.

RESULTS

Results from 153 consecutive patients (65 male, 88 female) were evaluable. The majority (65%) of chiasmal lesions was due to pituitary adenoma, followed by craniopharyngioma (12%), astrocytoma (9%), and meningioma (8%). Vascular lesions in this region occurred rarely (2%). Three per cent of all patients had no final diagnosis. The majority (22%) of scotomas was attributable to involvement of the temporal hemifield in both eyes, with true bitemporal hemianopia being a very rare event (1%). Anterior junction syndrome, characterized by advanced visual field loss affecting the visual field centre in one eye and (possibly subtle) defects respecting the vertical midline in the fellow eye, was the second most frequent classifiable VFD (13%). Homonymous hemianopic VFDs occurred in 11% of all cases. Nine per cent of all patients exhibited monocular VFDs which did not respect the vertical midline, whereas in 3% of the subjects the monocular VFDs did not cross the vertical meridian. Binasal defects and posterior junction syndrome also occurred seldom (< 1%). Nineteen per cent of all visual field records of patients with chiasmal lesions had results, which could not be classified unequivocally, and an identical portion was rated normal.

CONCLUSION

In patients with chiasmal lesions, incomplete involvement of the temporal hemifields in both eyes was the most frequent event (22%), followed by anterior junction syndrome (13%). The latter entity at least clinically indicates the proximity of the pre-chiasmal ipsilateral optic nerve and decussating fibres emanating from the inferior nasal hemiretina of the fellow eye. However, this cannot provide conclusive evidence for the existence of anterior Wilbrand's knee.

Ink-jet printing for micropattern generation of laminin for neuronal adhesion

In order to achieve defined adhesion and neurite outgrowth, the growth substrate must be patterned in an appropriate way. We utilised ink-jet printing by means of a piezo-based microdispenser to create defined line patterns of a polymer with typical dimensions of 100 microm width on glass, silicon, gold and carbon substrates. Vinnapas, a co-polymer of vinyl acetate and ethylene, was mixed with the extracellular matrix protein laminin to achieve neuronal adhesion on the surface of the patterns. It could be demonstrated that the laminin entrapped in the polymer lines can be recognised by a specific antibody. Adhesion of embryonic chicken forebrain neurones is following the prepared lines, and identity of adhering cells could be shown by neurofilament staining. These findings open the route for the generation of complex small neuronal arrays and for the electrochemical investigation of the obtained neuronal matrix.

Retinal ganglion cells resistant to advanced glaucoma: a postmortem study of human retinas with the carbocyanine dye DiI

PURPOSE

The present study was conducted to examine whether the morphology of the retinal ganglion cells is altered in advanced glaucoma. Perikaryal, axonal, and dendritic alterations were monitored in glaucoma-resistant retinal ganglion cells by postvitam application of the fluorescent dye DiI.

METHODS

The retinas of four amaurotic glaucomatous eyes and four normal eyes enucleated after death were used in this study. The retinas were freed from surrounding tissue, prepared as flatmounts on a nitrocellulose filter, and fixed overnight in 4% paraformaldehyde. The retinal ganglion cells were labeled by introducing crystals of the fluorescent carbocyanine dye DiI, into the optic fiber layer. This dye diffuses along membranes of ganglion cell axons, completely labeling them and their cell bodies and dendrites. Further characterization of the retinas and optic nerves included hematoxylin-eosin and van Gieson histochemical staining as well as immunohistochemistry against glial fibrillary acidic protein.

RESULTS

Because of the advanced stage of the disease, the retinas were almost completely depleted of ganglion cells, which had degenerated and therefore could not be stained. The few remaining ganglion cells were considered to be resistant to glaucoma. They showed drastic morphologic alterations, such as abnormal axonal beading, the cell bodies were normal in size but had irregular silhouettes or swellings, and there were fewer dendritic bifurcations. The size of the dendritic trees was smaller, implicating pruning of smaller dendritic branches. Glial cells were also detected immunocytochemically indicating their involvement in the pathologic course of glaucoma.

CONCLUSIONS

The data suggest that the few ganglion cells that survive the elevated intraocular pressure associated with loss of visual function display morphologic changes that are manifested both on the cell body and on their intraretinal processes, including axons and dendrites.

UV irradiation causes multiple cellular changes in cultured human retinal pigment epithelium cells

BACKGROUND

The retinal pigment epithelium maybe causally involved in the development and progression of age-related macula degeneration; however, the mechanisms leading to the development of age-related macula degeneration remain largely unknown. The purpose of this study was to examine cellular changes in the retinal pigment epithelium induced by direct irradiation with UV light in culture.

METHODS

Retinal pigment epithelium cells from post-mortem human retinas were used to obtain dissociated cultures with cells retaining the ability to differentiate in vitro. These cells were cultured over several days to weeks. The UV radiation (UV-A and UV-B) occurred under sterile conditions with a 100 HBO/mercury bulb attached to a dissecting microscope, delivering co-axial illumination. The time dependence of irradiation effects was analysed using morphometric, immunohistochemical, functional and apoptosis-detecting techniques.

RESULTS

Vital and proliferating retinal pigment epithelium cell cultures could be prepared consistently. The cells showed tissue-specific morphologies in vitro for several days to weeks. Pigment epithelium-derived factor was detected in these cells using immunocytochemistry and Western blots. The UV irradiation but not white light resulted in measurable alterations of cell shape and size. The irradiated cells showed partial swelling and shrinkage reminiscent of progressing apoptotic degeneration. TUNEL staining revealed that apoptosis was induced by UV light, but not detectably by white light. The phagocytosis of fluorescent micro-particles diminished after irradiation. These effects were dependent on the duration of irradiation.

CONCLUSIONS

Cultures of retinal pigment epithelium are suitable and sensitive models to study cell damage and may contribute to unravelling the pathogenetic mechanisms of retinal degeneration.

AMOG/beta2 and glioma invasion: does loss of AMOG make tumour cells run amok?

The beta2 subunit of Na,K-ATPase, initially described as adhesion molecule on glia (AMOG), has been shown to mediate neurone-astrocyte adhesion as well as neural cell migration in vitro. We have investigated the expression of AMOG/beta2 in human gliomas and its effect on glioma cell adhesion and migration. Compared to normal astrocytes of human brain, AMOG/beta2 expression levels of neoplastic astrocytes were down-regulated in biopsy specimens and inversely related to the grade of malignancy. One rat and four human glioma cell lines showed complete loss of AMOG. To investigate the function of AMOG/beta2, its expression was re-established by transfecting an expression plasmid into AMOG/beta2-negative C6 rat glioma cells. In vitro assays revealed increased adhesion and decreased migration on matrigel of AMOG/beta2-positive cells as compared to their AMOG/beta2-negative counterparts. We conclude that increasing loss of AMOG/beta2 during malignant progression parallels and may underlie the extensive invasion pattern of malignant gliomas.

Regeneration of ganglion cell axons into a peripheral nerve graft alters retinal expression of glial markers and decreases vulnerability to re-axotomy

PURPOSE

To compare the effect of cutting the optic nerve versus replacing the cut optic nerve with a peripheral nerve (PN) graft on retinal glial markers, and to determine whether the PN graft can stabilize regenerating retinal ganglion cells (RGCs), thus preventing their death following re-axotomy.

METHODS

Retinas harvested after ganglion cell regeneration into a sciatic nerve graft were compared to untreated control retinas and retinas obtained following optic nerve axotomy. Glial-specific proteins such as glial fibrillary acidic protein (GFAP), Bcl-2 and complement-3 receptor (Ox-42) were examined using immunohistochemistry. Ganglion cells that survived the second axotomy were quantified on retinal flat mounts by retrograde labeling from the graft.

RESULTS

GFAP expression in astrocytes and Muller cells was elevated in axotomized retinas when compared to controls, and an additional up-regulation in Muller cells was found in retinas following ganglion cell regeneration. Increased GFAP expression in retinas containing regenerated neurons was accompanied by increased Bcl-2 expression with latter being confined to Muller cells. Moreover, re-axotomy of the regenerated axons within the graft did not result in significant retrograde degeneration of RGCs within 28 days.

CONCLUSIONS

The data suggest that the graft stabilizes the regenerating RGCs to an extent reminiscent of peripheral neurons, a process that may involve the interaction between neuronal and glial elements.

Measurement of nitric oxide production by the lesioned rat retina with a sensitive nitric oxide electrode

Nitric oxide (NO) plays multiple roles in the nervous system. It is produced as a result of damage or injury of the retina as a part of the central nervous system. Detailed knowledge of the extent and the time course of NO production is of great importance for the understanding of pathological processes and their appropriate medical treatment. Sections of rat retina were stained with antibodies against the three isoforms of NO synthase (NOS) at several time points after a lesion of the optic nerve. No significant changes of NOS expression could be seen at any of the checked time points. For the electrochemical detection of NO production, we modified small platinum electrodes with a NO-sensitive nickel porphyrin by electrochemical polymerisation. Compared to other substances, electrochemically polymerised eugenol was found to be most suitable for protection against interferences. For the measurements, differential pulse amperometry was used. The response to nitric oxide was linear.NO production of adult rat retinas was measured post axotomy after different time points with electrochemical electrodes ex vivo. With non-treated retinas, an NO concentration of approximately 15 microM was measured. NO concentration is elevated after an axotomy reaching its highest value of up to 30 microM 5 days after the lesion. The NO concentration is decreased below the initial value after 9-14 days post axotomy.

Sodium dodecyl sulfate versus acid-labile surfactant gel electrophoresis: comparative proteomic studies on rat retina and mouse brain

A long-chain derivative of 1,3-dioxolane sodium propyloxy sulfate, with similar denaturing and electrophoretic properties as SDS, and facilitated protein identification following polyacrylamide gel electrophoresis (PAGE) for Coomassie-stained protein bands, has been tested. Comparative acid-labile surfactant/sodium dodecyl sulfate two-dimensional (ALS/SDS 2-D)-PAGE experiments of lower abundant proteins from the proteomes of regenerating rat retina and mouse brain show that peptide recovery for mass spectrometry (MS) mapping is significantly enhanced using ALS leading to more successful database searches. ALS may influence some procedures in proteomic analysis such as the determination of protein content and methods need to be adjusted to that effect. The promising results of the use of ALS in bioanalytics call for detailed physicochemical investigations of surfactant properties.

Benzodiazepine and kainate receptor binding sites in the RCS rat retina

BACKGROUND

The effect of age and photoreceptor degeneration on the kainate subtype of glutamate receptors and on the benzodiazepine-sensitive gamma-aminobutyric acid-A receptors (GABA(A)) in normal and RCS (Royal College of Surgeons) rats were investigated.

METHODS

[(3)H]Kainate and [(3)H]flunitrazepam were used as radioligands for kainate and GABA(A)/benzodiazepine()receptors, respectively, using the quantitative receptor autoradiography technique.

RESULTS

In both normal and RCS rat retina we observed that [(3)Eta]flunitrazepam and [(3)Eta]kainate binding levels were several times higher in inner plexiform layer (IPL) than in outer plexiform layer (OPL) at all four ages studied (P17, P35, P60 and P180). Age-related changes in receptor binding were observed in normal rat retina: [(3)Eta]flunitrazepam binding showed a significant decrease of 25% between P17 and P60 in IPL,and [(3)Eta]kainate binding showed significant decreases between P17 and P35 in both synaptic layers (71% in IPL and 63% in OPL). Degeneration-related changes in benzodiazepine and kainate receptor binding were observed in RCS rat retina. In IPL, [(3)Eta]flunitrazepam and [(3)Eta]kainate binding levels were higher than in normal retina at P35 (by 24% and 86%, respectively). In OPL, [(3)Eta]flunitrazepam binding was higher in RCS than in normal retina on P35 (74%) and also on P60 (62%).

CONCLUSIONS

The results indicate that postnatal changes occur in kainate and benzodiazepine receptor binding sites in OPL and IPL of the rat retina up to 6 months of age. The data also suggest that the receptor binding changes observed in the RCS retina could be a consequence of the primary photoreceptor degeneration.

Isolation of total-RNA from formalin-fixed rat retina

The aim of this project was to establish a method for the purification of total-RNA from fixed rat-retina. Two different established methods were used for RNA purification, and successful isolation was verified with RT-PCR for amplification of beta-actin (two different product-lengths) and subsequent gel-electrophoresis. Total-RNA was successfully isolated from fixed rat-retina. The house keeping gene, beta-actin could be detected after fixing the retina either with 1% formalin or with 4% paraformaldehyde (PFA). Hexamer-primer based RT-PCR gave better results than the oligo-d(T)-primer based RT-PCR method. Both the 698 and 225 bp beta-actin-fragments could be successfully amplified, where amplification of the latter was more efficient. This approach shows that tissue fixation prior to RNA-isolation facilitates the rapid isolation of undamaged RNAs in tissues such as the retina, which are known to yield low levels of RNA and are vulnerable to RNases.

Detection of early neuron degeneration and accompanying microglial responses in the retina of a rat model of glaucoma

PURPOSE

To characterize the early reaction of retinal ganglion cells (RGCs) in a rat model of glaucoma using in vivo imaging and to examine the involvement of retinal microglia in glaucomatous neuropathy.

METHODS

Glaucoma was induced in adult female Sprague-Dawley rats by cauterizing two episcleral veins, which resulted in a 1.6-fold increase in intraocular pressure (IOP). Retinal ganglion cells were retrogradely labeled with the fluorescent dye, 4-[didecylaminostyryl]-N-methyl-pyridinium-iodide (4-Di-10ASP) and monitored in vivo after elevation of IOP using fluorescence microscopy imaging. The number of RGCs was quantified on retinal flatmounts. Dying RGCs were surrounded by activated microglia that became visible after taking up the fluorescent debris. Immunocytochemistry was conducted to characterize further the ganglion cells and microglia.

RESULTS

Cauterizing two of the four episcleral veins resulted in a consistent increase of IOP to 25.3 +/- 2.0 mm Hg, as measured with a handheld tonometer. IOP remained high for at least 3 months in glaucomatous eyes. The earliest sign of RGC death was detected in anesthetized animals 20 hours after induction of glaucoma. RGCs continued to decrease in number over time, with 40% of RGCs having degenerated after 2.5 months. Fundoscopic examination of the optic nerve head revealed cupping 2 months after induction of glaucoma. In addition, microglia were detected on retinal flatmounts as early as 72 hours after induction. Activated microglia and RGCs were also identified immunocytochemically, with an antibody against ionized calcium-binding adaptor molecule (Iba)-1 and an antibody specific to the 200-kDa subunit of the neurofilament protein, respectively.

CONCLUSIONS

Occlusion of episcleral veins is a reproducible method that mimics human glaucoma, with chronically elevated IOP-induced RGC loss. This study shows that in vivo imaging permits the detection of ganglion cells in the living animal in the early stages of the disease and highlights the importance of in vivo imaging in understanding ophthalmic disorders such as glaucoma. Secondly, activation of intraretinal microglia coincides with degeneration of RGCs in glaucoma.

In vivo FM: using conventional fluorescence microscopy to monitor retinal neuronal death in vivo

Post-traumatic death of mature retinal neurons occurs in glaucoma and after optic nerve injury. The death is a dynamic process that can be fully analyzed with methods that monitor changes over time. We have coupled the development of retrogradely transportable fluorescent dyes with modification of conventional epifluorescence microscopy to manipulate and visualize rat retinal neurons in vivo. The method is a relatively new concept and has potential for the monitoring of retinal conditions, such as glaucoma or optic nerve transection, and for evaluation of neuroprotective strategies in the near future.