Therapeutic Benefit of Radial Optic Neurotomy in a Rat Model of Glaucoma

Abstract

Radial optic neurotomy (RON) has been proposed as a surgical treatment to alleviate the neurovascular compression and to improve the venous outflow in patients with central retinal vein occlusion. Glaucoma is characterized by specific visual field defects due to the loss of retinal ganglion cells and damage to the optic nerve head (ONH). One of the clinical hallmarks of glaucomatous neuropathy is the excavation of the ONH. The aim of this work was to analyze the effect of RON in an experimental model of glaucoma in rats induced by intracameral injections of chondroitin sulfate (CS). For this purpose, Wistar rats were bilaterally injected with vehicle or CS in the eye anterior chamber, once a week, for 10 weeks. At 3 or 6 weeks of a treatment with vehicle or CS, RON was performed by a single incision in the edge of the neuro-retinal ring at the nasal hemisphere of the optic disk in one eye, while the contralateral eye was submitted to a sham procedure. Electroretinograms (ERGs) were registered under scotopic conditions and visual evoked potentials (VEPs) were registered with skull-implanted electrodes. Retinal and optic nerve morphology was examined by optical microscopy. RON did not affect the ocular hypertension induced by CS. In eyes injected with CS, a significant decrease of retinal (ERG a- and b-wave amplitude) and visual pathway (VEP N2-P2 component amplitude) function was observed, whereas RON reduced these functional alterations in hypertensive eyes. Moreover, a significant loss of cells in the ganglion cell layer, and Thy-1-, NeuN- and Brn3a- positive cells was observed in eyes injected with CS, whereas RON significantly preserved these parameters. In addition, RON preserved the optic nerve structure in eyes with chronic ocular hypertension. These results indicate that RON reduces functional and histological alterations induced by experimental chronic ocular hypertension.

Assessment of retinal ganglion cell damage in glaucomatous optic neuropathy: Axon transport, injury and soma loss

“…While the nuclear staining pattern of NeuN facilitates quantification in experimental GON (Belforte et al, 2012;Buckingham et al, 2008;Diaz et al, 2005;Naka et al, 2010), its lack of RGC specificity is a limitation. While Buckingham et al (2008) proposed methods to account for amacrine cells (identified by choline acetyltransferase, ChAT, IHC) when estimating RGC loss in mice, ChAT immunoreactivity varied with age (from 3 to 16% of cells in the GCL of DBA/2J mice 3e18 months old) and strain (DBA/2 vs. C57/BL6N), hence interpretation of results from studies employing NeuN can be problematic.…”

Detailed Evaluation of Possible Ganglion Cell Loss in the Retina of Zucker Diabetic Fatty (ZDF) Rats

“…1). Details about the statistics with the appropriate P values for each time point have already been given in another report 33 .

Figure 1Blood glucose levels in diabetic and lean ZDF rats. Blood glucose levels were significantly higher from postnatal week 7 till the end of the observation period.

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“…After fixation, the eyecups were rinsed several times with 0.1 M PB, the retinas were carefully detached with preserved orientation and threated further as whole mounts for RGC counting. The retinas were co-labelled with three different markers:Brn-3a 32,57,86 , NeuN 33 and RBPMS 34 that are known to recognize the majority of ganglion cells. The details about the primary antibodies used is given in Table 2.…”

The expression of syntaphilin is down-regulated in the optic nerve after axonal injury

“…In contrast to the optic nerve, syntaphilin IR was not co-localized with GFAP but was co-expressed with neuronal nuclei (NeuN) antigen, which is a marker for neurons ( Fig. 3) (Coelho et al, 2005;Belforte et al, 2012). Furthermore, syntaphilin co-localized with anti-post-density protein 95 (PSD 95), which is a marker for pre-synaptic sites (Fig.…”