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I. Soto, J. Son, N. Marsh-Armstrong; Proliferation and Oligodendrocyte Turnover in Optic Nerves of Glaucomatous DBA/2J Mice. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3687.
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Previous studies have suggested that oligodendrocytes die when axons are lost in the optic nerve. Indeed, some have suggested that oligodendrocyte loss is an early step in glaucoma pathology that precedes the loss of retinal ganglion cells. In order to explore whether early oligodendrocytes loss occurs in glaucoma, we analyzed the number of oligodendrocytes and astrocytes, as well as determined the extent of proliferation, in DBA/2J mice with different extents of pathology as well as similarly aged C57Bl/6J mice.
DBA/2J and C57Bl/6J mice of 2m and 9m of age were injected intraperitoneally with 0.1mg/Î¼l bromo-deoxy-uridine (BrdU) daily for five days and euthanized four hours after the last injection. Paraformaldehyde fixed optic nerves were embedded in OCT and sectioned. Longitudinal and transverse sections were processed for in situ hybridization with riboprobes detecting PLP and Vimentin mRNAs, as well as other markers for oligodendrocytes and optic nerve astrocytes, and with antibodies for BrdU, NG2, and Iba1 for microglial cells. Quantification of oligodendrocytes, astrocytes, NG2 cells, and BrdU positive cells were performed using custom scripts written for IPlab software.
Contrary to expectation, oligodendrocytes are not lost in substantial numbers from the optic nerves of DBA/2J mice, even those largely depleted of axons. Instead, excess oligodendrocytes are found among equally numerous astrocytes, the latter being highly reactive based on the high expression of Vimentin mRNA. However, oligodendrocytes in highly diseased optic nerves have, on average, lower expression of PLP. Diseased optic nerves also have large numbers of proliferating cells. The majority of the BrdU labeled cells are NG2 positive cells, astrocytes and oligodendrocytes expressing markers indicative of early stages of differentiation.
Counts of oligodendrocytes and astrocytes, counts of BrdU positive cells, and the determination of the fraction of BrdU positive cells that are labeled with cell type specific markers leads to the conclusion that in response to the loss of axons, there is a dramatic proliferative response in the glaucomatous optic nerve, principally in astrocytes and NG2-positive cells that produce oligodendrocytes.
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