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Y. H. Yucel, A. Darabie, P. L. Kaufman, N. Gupta; Astrocytes and NG-2 Glial Cells Are Activated in the Optic Tract of Experimental Primate Glaucoma. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3663. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To assess whether astrocytes and a novel glial cell called NG-2 are activated in the optic tract in glaucoma.
Eight macaque monkeys with unilateral experimental glaucoma with mean IOP of 57 ± 8.6 mmHg (± SD) over 5 to 33 weeks, were compared to normal controls (n=3). Optic tract specimens 2 mm from the LGN were cryoprotected, frozen and cut. Sections were double-labelled for glial fibrillary acidic protein (GFAP, Sigma and Dako) and chondroitin sulphate proteoglycan (NG-2, Chemicon) markers for astrocytes and NG-2 glia, respectively. Images were captured under confocal laser microscopy in a masked fashion, and percent supra-threshold area was measured as an index of immunofluorescence intensity (Image J software, NIH). The glaucoma group was compared to the control group using a t-test. Colocalization analysis was performed to determine overlap between NG2 and astrocyte marker (GFAP) and oligodendrocyte marker (myelin basic protein, Abcam).
Colocalization studies demonstrated that NG2 cells were distinctly different from oligodendrocytes and astrocytes, showing no overlap. NG-2 intensity index in the optic tract was significantly increased in glaucoma compared to controls (7.01 ± 3.4% vs. 0.54 ± 0.41 %, mean ± SD; p < 0.05). GFAP intensity index in the optic tract was also significantly increased in glaucoma group compared to controls (2.27 ± 1.49% vs. 0.08 ± 0.08 %; p < 0.05) for astrocytes.
NG-2 glial cells are a distinct population that is described for the first time in the primate optic tract, and shown to be activated in primate glaucoma. Astrocytes were also found to be activated in the optic tract containing the pre-geniculate retinal ganglion cell axons. The activation of these glial cells at the level of the optic tract likely contributes to ongoing glaucomatous injury and disease progression.
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