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M.J. Niittykoski, G. Kalesnykas, J. Rantala, R. Miettinen, K. Kaarniranta, A. Salminen, H. Uusitalo; The Effect of Increased Intraocular Pressure on Astrocytes in Rat Glaucoma Model . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3240.
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Human and experimental studies have found morphological changes and alterations in the expression of glial fibrillary acidic protein (GFAP) in astrocytes of glaucomatous retinas. One typical factor induced by stress, e.g. optic nerve transection, is synthesis of heat shock proteins (HSPs) that helps to maintain survival and functionality of cells. Therefore, the aim of the present study was to examine quantitative changes of retinal GFAP–immunoreactive cell population using stereology and response to stress induced by elevated intraocular pressure (IOP).
The IOP of adult male Wistar rats was elevated by laser photocoagulation of episcleral and limbal veins. The contralateral eye served as a control. The IOP was monitored using tonometer. A week later, one group of rats (n=4) was sacrificed and the laser treatment was repeated in the remaining of rats that were sacrificed 2 (n=4) or 3 (n=4) weeks after the first laser treatment. Thereafter, retinal astrocytes and HSP25 positive cells were visualized from flat–mounted retinas immunohistochemically. The GFAP and HSP25 colocalization was confirmed using laser scanning confocal devide. The total number of retinal astrocytes was estimated using stereology. In addition, silver stained sections of optic nerves of glaucomatous eyes were examined to reveal neurodegenerative changes.
There was a significant increase in the IOP after the laser treatment as compared to control eyes (the first week: 31.3±11.5 mmHg, the second week: 29.4±15.0 mmHg, the third week: 24.0±6.7 mmHg, mean±SD). Stereological counting indicated that laser–treated eyes had a decreased number of GFAP–immunoreactive cells by 42% after 3 weeks of elevated IOP. Furthermore, there was a 3–fold increase in the number of astrocytes that colocalize HSP25 in laser–treated eyes than that in controls. Finally, the silver staining revealed a significant increase of neurodegenerative material in the peripheral part of the optic nerve of glaucomatous eyes as compared to control specimens.
The present study demonstrates that the retinal astrocytes are damaged in response to elevated IOP.
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