Retinal Ganglion Cell Remodelling in Experimental Glaucoma

Abstract

Abstract: : Purpose:To explore the changes in retinal ganglion cell (RGC) morphology in a rodent model of experimental glaucoma. Methods: Experimental ocular hypertension was induced unilaterally in adult male Norwegian Brown rats by sclerosis of the episcleral drainage vessels with hypertonic saline (1.75 M). The contralateral eye acted as a control. Intraocular pressures were measured using a calibrated Tonopen XL (Mentor, USA) in animals maintained in a constant low light environment (40–90 lux). Animals (n=7) were sacrificed at selected time points (4–6 weeks) post induction of ocular hypertension. RGCs, in wholemount preparations of retinae, were labelled by biolistic delivery of tungsten microparticles coated with DiI (Molecular Probes), using a Helios BioRad Gene Gun. Cells were viewed by fluorescence microscopy and captured as digital images using Leica Q Fluoro. The dendritic trees of forty labelled RGCs (twenty in each group) were analysed using ImageJ (NIH). Modified Sholl analysis of the number of dendrites crossing the rings of defined diameter, centred on the cell soma, was performed using customised macros (Hollis Lab). Results: Episcleral vessel sclerosis produced a moderate and sustained rise in intraocular pressure (mean increase of 6.39 mmHg {SD: ±0.43}). IOP increases were seen in all animals. Optimal cell labelling was obtained by using 1.7µm tungsten beads injected at 120 psi pressure coated with DiI. Marked pruning of the dendritic tree of labelled RGCs in glaucomatous retinae was observed as compared to normal. This was demonstrated by the decline in RGC dendrite number from a mean of 11.77 (±6.34) dendrites in control retinae to 5.47(±4.36) dendrites in ocular hypertensive retinae (p<0.002). There was also a reduction in overall dendritic field diameter from 213.29µm (±54.84) in control retinae to 151.12µm (±49.8) in the glaucomatous group (p< 0.001). Conclusions: Biolistic labelling is an effective technique for the morphological analysis of retinal ganglion cells. Reductions in the size and complexity of the dendritic tree of RGCs were observed following induction of ocular hypertension in this rodent model of experimental glaucoma.

Keywords: retina: proximal (bipolar, amacrine, and ganglion cells) • pathology: experimental • intraocular pressure