Purpose:
To evaluate retinal ganglion cell (RGC) survival by quantifying Rbpms (RNA binding protein with multiple splicing)-immunolabeled cells in rat models of optic nerve injury and experimental glaucoma.
Methods:
Optic nerve crush, intravitreal injection of excitotoxin and trabecular laser photocoagulation were given to adult rats. Immunohistochemistry and topographic analysis of Rbpms immunolabeling were performed on the retinal wholemounts. Retrograde labeling with Fluorogold and double-labeling of III beta-tubulin were compared with Rbpms immunolabeling.
Results:
Density of Rbpms-positive cells decreased from the posterior pole to the peripheral adult rat retina. Compared to control eyes, 37%, 87% and 93% loss of Rbpms-positive cells were observed 1, 2, and 4 weeks after optic nerve crush. There were significant losses of Rbpms-positive cells 1 week after injection of 12, 30 and 120 nmoles N-methyl-D-aspartate (NMDA) while co-injection of MK-801 significantly preserved Rbpms-positive cells after 120 nmoles NMDA injection from 10% to 59% cell survival. Almost 100% Rbpms-positive cells were III beta-tubulin positive in these conditions. After 5 weeks of intraocular pressure (IOP) elevation induced by laser photocoagulation, significant loss of Rbpms-positive cells was noted (P<0.05). Cumulative IOP elevation was calculated by performing separate integrations of the IOP over the days of exposure for the experimental and contralateral control eyes. Remarkable regional loss of Rbpms-positive cells was observed if the cumulative dark-phase IOP elevation was below 100 mmHg-day while there was more dramatic loss of Rbpms-positive cells in the eyes with higher IOP. In the eyes with elevated IOP and contralateral controls, over 99% of Rbpms-positive cells were double-labeled with Fluorogold.
Conclusions:
Our findings indicate that Rbpms can be used for specific and reliable labeling of RGCs in the retina and evaluation of RGC survival in various animal models of RGC degeneration.
Keywords: ganglion cells • optic nerve • cell survival