title: Retinal damage after 3 to 4 months of elevated intraocular pressure in a rat glaucoma model.
abstract: OBJECTIVE
  To characterize a long-term elevated intraocular pressure (IOP) glaucoma model in the rat with respect to electroretinographic (ERG) changes and the pattern and mechanism of retinal ganglion cell (RGC) death. METHODS; An approximate doubling of IOP was induced in one eye (G) of female Wistar rats (150-180 g) by cautery of 3 episcleral/limbal veins. At intervals over 3 to 4 months, measurements of IOP and ERG changes (contact-lens electrode) were made in both the G and contralateral normal (N) eyes. At the end of 3 to 4 months of elevated IOP, RGCs were fluorescently labeled with Fluorogold (retrogradely from the superior colliculus), or retinas were labeled by intravitreal injection of a mitochondrial potential indicator dye and stained for apoptotic nuclei with a DNA dye. Flatmounts of fixed, dye-labeled retinas were examined by epifluorescence, confocal, or interference contrast microscopy.
  
  
  RESULTS
  Elevated IOP was consistently maintained for up to 4 months in G eyes, but ERG a- and b-waves showed a statistically significant decline, of 30% to 40% in amplitude, after 3 months. Loss of RGCs in G retinas was primarily focal with no statistically significant loss demonstrable outside of the focal areas when assessed by an area sampling method for counting RGCs, which totaled 2% to 3% of the entire retinal area. Mitochondrial membrane potential of cells in the RGC layer was reduced by 17.5% (P: < 0.05) in regions surrounding areas of focal loss compared with comparable locations in control N eyes. After 3.5 months' elevated IOP the G retinas showed cell nuclei at various stages of apoptosis, from initial DNA condensation to fragmentation.
  
  
  CONCLUSIONS
  The three-vein episcleral/limbal vein occlusion model for inducing glaucomatous pathology in the rat eye gives a consistent long-term elevation of IOP. After 3 to 4 months of approximately 100% increased IOP, the ERG responses begin to decline, there is a variable focal loss of RGCs, and some of the remaining RGCs show characteristics of stress and apoptosis. These changes seem consistent with retinal damage in human glaucoma (focal field defects), and this rat model appears to mimic some features of primary open-angle glaucoma.
authors.affiliation: Departments of Ophthalmology and. Neurology, Mount Sinai School of Medicine, New York University, New York 10029-6574, USA. thomas.mittag@mssm.edu
authors.forename: T W
authors.initials: TW
authors.lastname: Mittag
authors.forename: J
authors.initials: J
authors.lastname: Danias
authors.forename: G
authors.initials: G
authors.lastname: Pohorenec
authors.forename: H M
authors.initials: HM
authors.lastname: Yuan
authors.forename: E
authors.initials: E
authors.lastname: Burakgazi
authors.forename: R
authors.initials: R
authors.lastname: Chalmers-Redman
authors.forename: S M
authors.initials: SM
authors.lastname: Podos
authors.forename: W G
authors.initials: WG
authors.lastname: Tatton
mesh_terms: D000818:Animals; D016923:Cell Death; D002467:Cell Nucleus / Q000473:pathology; D053938:DNA Fragmentation; D004195:Disease Models, Animal; D004596:Electroretinography; D005260:Female; D005456:Fluorescent Dyes; D005902:Glaucoma, Open-Angle / Q000150:complications* / Q000503:physiopathology; D007429:Intraocular Pressure; D008564:Membrane Potentials / Q000502:physiology; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000502:physiology; D016202:N-Methylaspartate / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar; D012164:Retinal Diseases / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D012165:Retinal Ganglion Cells / Q000187:drug effects / Q000473:pathology* / Q000502:physiology; D013266:Stilbamidines; D013997:Time Factors
chemical_list: C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D005456:Fluorescent Dyes; D013266:Stilbamidines; D016202:N-Methylaspartate