Selective Fluorogold and Dextranamine Retrograde Labeling of Retinal Ganglion Cells in Glaucoma

Abstract

Abstract: : Purpose: Since it has been proposed that retrograde transport in retinal ganglion cells (RGC) is altered in glaucomatous damaged cells, we compared selective RGC labeling using two retrogradely transported tracers: fluorogold (FG), which is transported. Methods: We compared control eyes and eyes in which the intraocular pressure (IOP) was increased for 6 months by episcleral vein cauterization in both pigs and rats. Rats were distributed in two groups: control group : FG was injected into the optic nerve (ON) of the right eye, whereas DXT crystals were applied to the ON of the left eye; episcleral group 1 : the ON of both eyes of these animals were injected with a mixture of FG and DXT in solution; episcleral group 2 : RGCs were labeled by injecting DXT cristals into the ON of both eyes. In the adult pig, the IOP of the left eye was raised as described above. After 6 months, a mixture of FG and DXT was injected into the ON of both eyes. Rats and pigs were maintained alive for 1 or 2 days, respectively and retinas were subsequently processed. Images from fields corresponding to 1.6 % of the retina were acquired and RGCs were counted and measured. Results: The number of RGCs labeled by DXT was significantly lower than that labeled by FG. Thus, only 40 ± 2 % of rat RGCs which were identified by FG tracing were labeled with DXT. We did not observe differences in the number of RGCs labeled with DXT when it was injected or applied as crystals. On the other hand, the percentage of RGCs labeled with FG but not with DXT was found to be similar in control and glaucomatous eyes. Finally, analysis of RGC soma area showed that DXT predominantly labels large RGCs. Conclusions: DXT labels a subpopulation of rat and pig RGCs which are identified by FG. This selective labeling is observed when DXT is applied as crystals or injected in solution and is evident in control or glaucomatous eyes.

Keywords: ganglion cells • intraocular pressure • retina