Morphological characteristics of retinal ganglion cells in the giant panda (Ailuropoda melanoleuca) retina

Abstract

Purpose : Analyzing morphological characteristics of retinal ganglion cells in the giant panda.

Methods : A pair of eyeballs was immediately collected from a deceased adult panda and hemisected. The eyecups were fixed with 4% Paraformaldehyde at room temperature for one hour. Routine immunohistochemical staining techniques were applied to label both retinal ganglion cells (RGCs) and melanopsin expressing RGCs (mRGCs). RGCs were selectively labeled by RBPMS polyclonal antibody (custom-made by ProSci Inc, CA) and mRGCs were detected with a melanopsin antibody (custom-made by Pacific Immunology Corp., CA). Images of RGCs and mRGCs were processed and analyzed with commercial software (Adobe Photoshop and Microsoft Excel).

Results : The average retinal area was 373 mm² (Left: 388 mm², Right: 364 mm²). An avascular area centralis (AC) was observed at the temporal retina, where an estimated peak density of RGCs was 1257/mm² (Right: 1275/mm², Left: 1238/mm²). The average distance between the center of the AC and that of the optic disk (OD) was 4.26 mm (Right: 4.15mm, Left: 4.37mm). The average soma size at the AC was 15.87 ± 2.31 µm. An increase of soma size with eccentricity was noticed. We measured soma size of RGCs at four equal eccentricity retinal locations (3 mm from AC). It was observed that cells located in temporal retina were larger than those found in nasal retina (T: 22.74 ± 3.28 µm vs N: 17.41 ± 3.13 µm). RGCs in superior retina were larger than those observed in inferior retina (S: 20.90 ± 2.86 µm vs I: 18.07 ± 2.42 µm). mRGCs were detected at different retinal locations. Both M1 and M2 were encountered.

Conclusions : The present study suggests that the giant panda adopted a retinal structure that is essential for better visual acuity and binocular vision. However, in comparison with carnivores and primates, the density of cRGCs of this area is extremely low. Melanopsin expressing RGCs are present in the giant panda retina. These morphological characteristics could be important for understanding visual adaptation and evolution of this living fossil.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.