Spatial Distribution and Quantitative Analysis of Retinal Ganglion Cells in Adult Albino Rodents

Abstract

Purpose:: To analyze the spatial distribution and to quantify the population of retinal ganglion cells (RGCs) in adult albino mice and rats.

Methods:: In adult albino Sprague Dawley (SD) (180-200 g) (female, n=20) rats and or in adult swiss mice (30-45 g) (male, n=10), the population of RGCs were retrogradely labelled with 3% Fluorogold (FG) in 0.9% NaCl applied to both superior colliculi (SCi). One week later rodents were perfused, the retinas prepared as whole-mounts and examined and photographed under a fluorescence microscope (Axioscop 2 plus, Zeiss, Germany) equipped with a digital camera (ProgRes c10, Jenoptik, Germany) and a motorized stage, connected to an image analysis system with an automatic frame-grabber device (Image-Pro Plus, ver. 5.1.2) and a plug-in Scope-Pro, ver 5.0 (MediaCybernetics, Inc. USA). Retinas were imaged as a stack of 24-bit color images (154 frames per retina for rats and 140 for mice) using image-pro with the scope-pro plug-in 5.0; these images were montaged into a composite high resolution retinal map when required. Images are processed by specific macros written in IPP that apply a sequence of filters and transformations to each image of the stack in turn before finally counting the resulting cells and transferring the data to a spreadsheet for analysis. Graphic representation of the distribution of RGC densities within the retina were represented by a contour-plot (SigmaPlot 9.0 for Windows, SYSTAT Software Inc., USA) for each retina.

Results:: One week after FG application to both SCi the mean total number of RGCs in 37 SD rat retinas was (mean±SD) 81,486±4,339. In adult mice, the mean total number of RGCs in 10 retinas was 47,075±3,961. RGCs were distributed across the retinas with higher densities in the central retina. The contour plots of density distribution revealed both in rats and mice the presence in the superior retina of a region with the highest RGC densities. This region was located 1-2 mm dorsal to the optic disc and formed a low curvature arc that resembled a visual streak.

Conclusions:: Albino rats and mice show an area in the superior retina that contains the highest RGC densities and resembles a visual streak.

Keywords: ganglion cells • imaging/image analysis: non-clinical • neuroprotection