Abstract
Purpose :
To investigate whether retinal ganglion cells (RGCs) are immmunoreactive for RGR in postmortem human retinas and to characterize their morphology and location.
Methods :
Seven human postmortem eyes from the 5th, 6th, and 7th decades of life (mean age 61.4 years old) were obtained at autopsy from various eye banks. Eyes were either fixed in 10% formalin (paraffin) or 4% paraformaldehyde (frozen) within 12 hours, dissected at the horizontal meridian at the level of the optic nerve, processed for paraffin or frozen sectioning, and serially cut at 5 µm (paraffin) or 10 µm (frozen). Sections were immunostained with a primary rabbit polyclonal antibody for RGR opsin. An indirect immunoperoxidase staining method with an HRP-bound secondary (with DAB as the chromogen) was used for paraffin and an immunofluorescence (IF) protocol using an FITC-conjugated secondary antibody was used for the frozen retinas. Immunoperoxidase sections were examined on a bright field microscope and the IF sections were analyzed by confocal microscopy. RGCs were examined in the inner retina for immunoreactivity to the RGR opsin and characterized morphologically.
Results :
Both immunoperoxidase and immunofluoescent staining for RGR opsin revealed several RGCs in the inner retina of all postmortem eyes. The RGCs were located in the retinal ganglion cell layer, the inner plexiform layer, and the inner nuclear cell layer. The immunopositive cells were typically medium to large cells (15-30 µm in diameter), had positive staining in the soma, dendrites, and axons. The immunostaining was characterized as “punctate” in both paraffin and frozen samples and at times appeared as large focal aggregates. In what appeared as medium to large RGCs, both eccentric and centrally located nuclei were observed. Immunopositive axons were also identified in the retinal nerve fiber layer.
Conclusions :
These results demonstrate that the RGR opsin may be present in RGCs of the inner retina. Also, the morphology of these immunoreactive cells may indicate that RGR is expressed in different RGC subtypes. The presence of RGR in RGCs may possibly play an undiscovered role in the intrinsically photosensitive class of melanopsin ipRGCs and other RGC subtypes.
This is a 2020 ARVO Annual Meeting abstract.