Rita Naskar

Effects of anti-glaucoma medications on gangion cell survival: the DBA/2J mouse model

We studied whether several agents, approved or undergoing trials in human glaucoma, were effective in preventing ganglion cell loss in the DBA/2J mouse. Adult DBA/2J mice were treated with timolol, pilocarpine, brimonidine, dorzolamide, or NMDA-receptor antagonist memantine. Surviving retinal ganglion cells of treated and control mice were retrogradely labeled with fluorogold and counted after whole mount preparation. In treated mice, only memantine and timolol had significant effects on retinal ganglion cell survival (P<0.0001, analysis of variance). Brimonidine was lethal to these mice, and these retinae were not analyzed further. The DBA/2J mouse represents a promising candidate for further experimentation in ocular hypertension.

New horizons in neuroprotection.

Glaucoma is a leading cause of blindness worldwide and the second leading cause of irreversible blindness in the USA. The most common form of glaucoma, primary open angle glaucoma, is characterized by a chronically elevated intraocular pressure in the absence of any demonstrable structural abnormalities in the eye. The pathologic hallmark of glaucomatous optic neuropathy is the selective death of retinal ganglion cells associated with structural changes in the optic nerve head. Recent discoveries suggest a role for nitric oxide, glutamate, apoptosis, and others, in the pathophysiology of this neuropathy. These newer discoveries are addressed in this article.

Adeno-associated viruses containing bFGF or BDNF are neuroprotective against excitotoxicity

Purpose. Brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (bFGF) hold much promise for the protection of retinal ganglion cells against excitotoxic cell death. We tested the possibility of delivering these growth factors to retinal ganglion cells via an adeno-associated viral (AAV) vector and tested their efficacy in two models of excitotoxicity. Methods. Rat retinas were infected with AAV vectors encoding bFGF or BDNF. A control vector containing green fluorescent protein (GFP) was injected in the contralateral eye. Eyes were subjected to either an intravitreal injection of N-methyl-D-aspartate (NMDA) or optic nerve crush, and ganglion cell survival was evaluated. Results. AAV.CMV.bFGF and AAV.CBA.BDNF were neuroprotective against NMDA injection 1 month post-treatment. Additionally, AAV.CMV.bFGF was protective against optic nerve crush. Conclusion. AAV-mediated delivery of bFGF and BDNF can promote retinal cell survival following excitotoxic insult.

Early electroretinographic features of streptozotocin-induced diabetic retinopathy

Background:  This study set out to document the early electrophysiological and immunohistochemical changes that occur in the retina of experimentally induced diabetic rats.

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.

Saving the Nerve from Glaucoma: Memantine to Caspaces

Three recent discoveries regarding the pathophysiology of human glaucoma are that retinal ganglion cells die by apoptosis, that nitric oxide synthase levels are altered, and that glutamate is elevated in the vitreous. These findings provide encouraging new avenues for the development of neuroprotective strategies to alleviate ganglion cell loss and blindness that accompanies this disease. In this article, we discuss some of these data, as well as potential therapies that may arise from these findings.

THY-1 IS CRITICAL FOR NORMAL RETINAL DEVELOPMENT

In the mammalian retina, Thy-1, the most abundant mammalian neuronal surface glycoprotein, is found predominantly if not exclusively on retinal ganglion cells. We hypothesized that Thy-1 plays a significant role in retinal development. Neurite outgrowth of retinal ganglion cells from Thy-1(-) mice over multiple substrates was compared to that seen with wild-type controls. Adult mouse retinas were histologically compared between Thy-1(-) and three strains of Thy-1 positive mice. Thy-1(-) retinal ganglion cells had significantly less neurite outgrowth than controls. The inner nuclear, inner plexiform, ganglion cell and outer segment/pigment epithelium layers were thinner in Thy-1(-) retinae than in controls. Thy-1 appears to be critical for normal retinal development.

Transformation of adult retina from the regenerative to the axonogenesis state activates specific genes in various subsets of neurons and glial cells.

The purpose of this study was to identify the gene expression profile of the regenerating retina in vitro. To achieve this goal, three experimental groups were studied: (1) an injury control group (OC‐LI group) that underwent open crush (OC) of the optic nerve and lens injury (LI) in vivo; (2) an experimental group (OC‐LI‐R group) that comprised animals treated like those in the OC‐LI group except that retinal axons were allowed to regenerate (R) in vitro; and (3) an experimental group (OC‐LI‐NR group) that comprised animals treated as those in the OC‐LI group, except that the retinas were cultured in vitro with the retinal ganglion cell (RGC) layer facing upwards to prevent axonal regeneration (NR). Gene expression in each treatment group was compared to that of untreated controls. Immunohistochemistry was used to examine whether expression of differentially regulated genes also occurred at the protein level and to localize these proteins to the respective retinal cells. Genes that were regulated belonged to different functional categories such as antioxidants, antiapoptotic molecules, transcription factors, secreted signaling molecules, inflammation‐related genes, and others. Comparison of changes in gene expression among the various treatment groups revealed a relatively small cohort of genes that was expressed in different subsets of cells only in the OC‐LI‐R group; these genes can be considered to be regeneration‐specific. Our findings demonstrate that axonal regeneration of RGC involves an orchestrated response of all retinal neurons and glia, and could provide a platform for the development of therapeutic strategies for the regeneration of injured ganglion cells.

Benzodiazepine and kainate receptor binding sites in the RCS rat retina

BackgroundThe effect of age and photoreceptor degeneration on the kainate subtype of glutamate receptors and on the benzodiazepine-sensitive γ-aminobutyric acid-A receptors (GABAA) in normal and RCS (Royal College of Surgeons) rats were investigated.Methods[3H]Kainate and [3H]flunitrazepam were used as radioligands for kainate and GABAA/benzodiazepinereceptors, respectively, using the quantitative receptor autoradiography technique.ResultsIn both normal and RCS rat retina we observed that [3Η]flunitrazepam and [3Η]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: [3Η]flunitrazepam binding showed a significant decrease of 25% between P17 and P60 in IPL ,and [3Η]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, [3Η]flunitrazepam and [3Η]kainate binding levels were higher than in normal retina at P35 (by 24% and 86%, respectively). In OPL, [3Η]flunitrazepam binding was higher in RCS than in normal retina on P35 (74%) and also on P60 (62%).ConclusionsThe 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.