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Roman Blanco, Juan Gros, Laura Ramirez, Marcelino Avilés - Trigueros, Consuelo Perez-Rico; A new experimental rat model of chronic pressure-induced optic nerve damage by polidocanol injection in the aqueous humor outflow pathway. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2411.
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In this study we describe a highly effective method of injecting polidocanol, a foamed sclerosant drug, in the aqueous humor outflow pathway, to induce a moderate and persistent elevated intraocular pressure (IOP) and optic nerve damage in rats.
Unilateral elevation of IOP was produced by polidocanol injection into perilimbal veins in adult NMRI rats using 10 μl borosilicate glass micropipettes made with a P-97 Flaming/ Brown Micropipette puller. After rats were anesthesized by isoflurane inhalation, the conjunctive was carefully dissected and perilimbal veins were exposed. Polidocanol was slowly injected in the limbal vascular plexus with a force just enough to blanch the vessels. IOP was measured every other day at the same time in both eyes using a tonometer TonoLab (Icare). Optic nerve and retina functional and structural damage were assessed with full-field scotopic and photopic electroretinograms (ERGs) and Brn3A Inmunohistochemistry in flat-mounted retina preparations and standardized automated retinal ganglion cell (RGC) counts.
A single injection of perilimbal polidocanol induced a moderate IOP elevation up to four weeks, without causing overt ocular structure damage or inflammatory responses while inducing RGC and axon degeneration that simulated glaucomatous changes. Among experimental eyes, the group average IOP (± SD) was 23 ± 6.6 mmHg whereas for control eyes was 12.1 ± 1.4 mmHg (t=3.7, P<0.02) under isoflurane anesthesia. There was a selective reduction of the positive scotopic negative response (pSTR) whereas other ERG components remained unaltered indicating no damage to the outer retina. RGC functional injury occurred before the onset of structural damage, as assessed by light microscopy. With time, significant reductions of RGC number and densities were noted in the experimental eyes compared with the contralateral control eyes, as revealed by BR3nA e labeling. RGC loss followed a retinotopic fashion, in which the superior region of the optic nerve region was damaged first.
This new experimental rat model shows a moderate and consistent increased IOP, death of RGC but not other retinal neurons, lack of adverse effects on the cornea and sclera and low-cost of implementation.
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