An unconventional distribution pattern of retinal ganglion cells in the giant panda (Ailuropoda melanoleuca)

PURPOSE:: Characterize the vertical distribution pattern of retinal ganglion cells in the giant panda.
 Methods: Four eyeballs were immediately collected from deceased adult pandas. Routine immunohistochemical staining techniques were applied to label retinal ganglion cells (RGCs). RNA-binding protein with multiple splicing (RBPMS) was used as an RGC marker to selectively label RGCs (custom-made by ProSci Inc, CA) and SMI-32 was used as an Alpha RGC marker. Immunostained RGCs were scanned under confocal microscopy and analyzed with commercial software (Adobe Photoshop and Microsoft Excel). RESULTS: As expected, the isodensity map of RGCs in the cat exhibited a typical horizontally positioned visual streak, in contrast, that of the panda showed a vertically oriented isodensity RGCs band. This band crossed the center of AC-like peak density region and extended vertically from the superior to the inferior retina (5.22 ± 0.46 mm, n=3). The averaged width of the band was 2.18 ± 0.32 mm (n=3). SMI-32 positive RGCs were also analyzed, accordingly. CONCLUSION: The present study suggests that the giant panda adopted a retinal structure that is essential for better visual performance and survival. These morphological characteristics of RGCs could be important for understanding visual adaptation and evolution of this living fossil.