Abstract
ABSTRACT Purpose A major challenge in glaucoma research is the lack of reproducible animal models of RGC and optic nerve damage, the characteristic features of this condition. We therefore examined the glaucomatous responses of two different rat strains, the Brown Norway (BN) and Lister Hooded (LH) rats, to high intraocular pressure (IOP) induced by injection of magnetic beads into the anterior chamber. Methods Magnetic microsphere suspensions (20 µl of 5–20 mg/ml) were injected into the anterior chamber of BN (n = 9) or LH (N = 15) rats. Animals from each strain were divided into three groups, each receiving a different dose of microspheres. IOP was measured over 4 weeks using a rebound tonometer. Retinal ganglion cell (RGC) damage and function were assessed using scotopic electroretinograms (ERGs), retinal flatmounts and optic nerve histology. ANOVA and Student’s t-tests were used to analyse the data. Results A significant elevation in IOP was observed in BN rats receiving injections of 20 mg (37.18 ± 12.28 mmHg) or 10 mg microspheres/ml (36.95 ± 13.63 mmHg) when compared with controls (19.63 ± 4.29 mmHg) (p < .001) over 2 weeks. This correlated with a significant impairment of RGC function, as determined by scotopic ERG (p < .001), reduction in axon number (p < .05) and lower RGC density (P < .05) in animals receiving 20 mg or 10 mg microspheres/ml as compared with controls. LH rats receiving similar microsphere doses showed reduced scotopic ERG function (p < .001) after 2 weeks. No changes in IOP was seen in this strain, although a reduction in axon density was observed in optic nerve cross-sections (p < .05). Initial changes in IOP and ERG responses observed in BN rats remained unchanged for a duration of 7 weeks. In LH animals, ERG responses were decreased at 1–2 weeks and returned to control levels after 5 weeks. Conclusions Although this model was easily reproducible in BN rats, the phenotype of injury observed in LH rats was very different from that observed in BN animals. We suggest that differences in the glaucomatous response observed in these two strains may be ascribed to anatomical and physiological differences and merits further investigation.
Highlights
It is well accepted that raised intraocular pressure (IOP) is a risk factor that underlies the onset and progression of retinal ganglion cell (RGC) axon degeneration associated with glau comatous optic neuropathy,[1] the mechanisms that lead to the pathophysiology of glaucoma are not fully under stood
This study evaluated the model of high intraocular pressure induced by magnetic microsphere injection into the anterior chamber of the eye in two different rat strains, the Brown Norway rat and the Lister Hooded rat
The negative scotopic threshold response (nSTR) ana lysis revealed that injections of both 20 mg and 10 mg microspheres/ml caused a significant decrease in RGC function (p < .001) (Figure 2b)
Summary
It is well accepted that raised intraocular pressure (IOP) is a risk factor that underlies the onset and progression of retinal ganglion cell (RGC) axon degeneration associated with glau comatous optic neuropathy,[1] the mechanisms that lead to the pathophysiology of glaucoma are not fully under stood. Several experimental models have been used to investi gate the molecular and biological mechanisms that lead to IOPinduced optic nerve injury, but they frequently recreate differ ent aspects of the disease.[2] It is generally recognised that there is not an ideal model that accurately mimics all the features of human glaucoma,[2] for which much research is still needed. Current animal models of glaucoma include those that naturally develop, such as the DBA/2 J mouse, as well as experimentally induced models. DBA/2 J mice spontaneously develop glaucoma-like features, including increased IOP and RGC loss after 3 months of age,[4] they show variability in disease progression, and RGC damage may not correlate with increased IOP.[5] Experimentally induced models of glaucoma have been developed in order to understand the natural history of human disease
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