Three experimental glaucoma models in rats: Comparison of the effects of intraocular pressure elevation on retinal ganglion cell size and death
Introduction
Elevated intraocular pressure (IOP) is one of the most important risk factors for developing glaucoma. In order to understand in detail the mechanisms which take place in glaucoma and lead to retinal damage, fast, inexpensive and reproducible animal models need to be developed (Chew, 1996).
The currently available models of experimental glaucoma involve the induction of a chronic increase in IOP. This increase can be achieved by reducing aqueous humor outflow through the eye. Thus, aqueous humor drainage can be interrupted by cauterizing two or three episcleral veins (Shareef et al., 1995) or by injecting hypertonic saline into the episcleral veins in rats (Morrison et al., 1997). Moreover, laser energy has been employed as a tool to perform burns directed at the trabecular meshwork (TM) (Ueda et al., 1998) and at both TM and episcleral veins (Levkovitch-Verbin et al., 2002). Other methods are based on the blockage of aqueous humor drainage at the level of the trabecular meshwork, avoiding manipulation of the eye vascular system. Thus, injection of different substances such as ghost red blood cells (Quigley and Addicks, 1980) or latex microspheres into the eye anterior chamber (Weber and Zelenak, 2001) leads to TM channel blockade. Finally, injection of viscoelastic agents into the eye anterior chamber has been reported to induce IOP spikes by a mechanical obstruction of the trabecular meshwork in rabbits (Benson et al., 1983, Manni et al., 1996, Törngren et al., 2000).
It has been widely demonstrated that retinal ganglion cells (RGCs) are selectively affected during glaucoma. However, few works have analyzed the pattern of RGC death by means of quantification of specifically labeled RGCs (Ko et al., 2001, Morgan et al., 2000, Naskar et al., 2002, Shareef et al., 1995). In this sense, during the first 10 weeks after IOP increase in rats, the rate of RGC death has been estimated to be uniform and almost linear at about 3–4% per week, but the degree of cell death seems to depend on the retinal region analyzed (Laquis et al., 1998).
Apart from RGC death, changes in RGC soma size have been reported in experimental glaucoma. Thus, an overall hypertrophy of all RGC types has been reported in rats after IOP elevation by episcleral vein cauterization (Ahmed et al., 2001). This increase in RGC soma size is also observed after optic nerve crush and axotomy (Moore and Thanos, 1996, Rousseau and Sabel, 2001). The increase in RGC soma size is likely to be in part a response to the space made available by the culling of RGC (Ahmed et al., 2001).
Glaucoma is a chronic and progressive disease and consequently, it is vital to develop experimental models which analyze RGC death following different periods of sustained elevation of IOP. The effect of experimental IOP elevation on RGC death has been analyzed during periods no longer than 12–16 weeks, due to the transitory effect of surgery. The main aim of the present study was to compare the effect of three different glaucoma models on RGC death and soma size. Moreover, we have also compared the effect of different periods of elevation of IOP in the same experimental glaucoma model to determine if a correlation exists between the duration of IOP elevation and the extent of RGC death.
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Animals
Twenty-one female Sprague–Dawley rats weighing 250–300 g were used in the present work. Animals were housed in a standard animal room with food and water provided ad libitum, a constant temperature of 21 °C and a 12-h light/dark cycle. All animal experimentation adhered to the ARVO Statement for the use of Animals in Ophthalmic and Vision Research.
Experiments were designed and carried out in such a way as to minimize animal suffering in accordance with European Communities Council Directive of 24
IOP increase
In control animals, the mean IOP was similar in both the right (23.06 ± 0.8 mmHg) and left eye (23.59 ± 0.7 mmHg) throughout all the experimental period (p = 0.61) (Fig. 1A).
Injections of latex microspheres into the eye anterior chamber led to a significant increase in IOP. Thus, the mean IOP in injected eyes was 28.1 ± 0.7 mmHg during the experimental period and this increase reached maximum values during the 27th week when the average IOP during this period was 1.69 times that of the control (37.6 ± 2.6
Discussion
IOP measurements were made using a tonopen XL applanation tonometer, which permits non-invasive determinations of IOP (Moore et al., 1993). Following the methodology used by others (Benozzi et al., 2002, Cohan and Bohr, 2001, Jia et al., 2000a), IOP measurements were performed using only topical anesthesia, thus avoiding any hypotensive (Jia et al., 2000b) or even neuroprotective effects (Fujikawa, 1995, Ozden and Isenmann, 2004) associated with general anesthesia. IOP determinations were
Acknowledgements
Grants from The Glaucoma Foundation (TGF 2004), ONCE (III Convocatoria I+D), First Price FUNDALUCE 2005, Spanish Ministry of Science and Technology (BFI 2003-07177) and the University of the Basque Country (E15350/2003).
References (40)
- et al.
Effects of increased intraocular pressure on rat retinal ganglion cells
Int. J. Dev. Neurosci.
(2001) - et al.
Electroretinographic abnormalities in a rat glaucoma model with chronic elevated intraocular pressure
Exp. Eye Res.
(2001) - et al.
Temporary elevation of the intraocular pressure by cauterization of vortex and episcleral veins in rats causes functional deficits in the retina and optic nerve
Exp. Eye Res.
(2003) - et al.
Patterns of retinal ganglion cell survival after brain-derived neurotrophic factor administration in hypertensive eyes of rats
Neurosci. Lett.
(2001) Architectural design of a self-sealing corneal tunnel, single-hinge incision
J. Cataract. Refract. Surg.
(1994)- et al.
The patterns of retinal ganglion cell death in hypertensive eyes
Brain Res.
(1998) - et al.
Differential increases in rat retinal ganglion cell size with various methods of optic nerve lesion
Neurosci. Lett.
(1996) - et al.
A rat model of chronic pressure-induced optic nerve
Exp. Eye Res.
(1997) - et al.
The pig eye as a novel model of glaucoma
Exp. Eye Res.
(2005) - et al.
Chronic ocular hypertension following episcleral venous occlusion in rats
Exp. Eye Res.
(1995)
Intraocular pressure development in the rabbit eye after aqueous exchange with ophthalmic viscosurgical devices
J. Cataract Refract. Surg.
Experimental glaucoma model in the rat induced by laser trabecular photocoagulation after an intracameral injection of India ink
Jpn. J. Ophthalmol.
Experimental glaucoma in the primate induced by latex microspheres
J. Neurosci. Methods
Effect of disinsertion of rectus eye muscles on aqueous humor composition i n rabbits
Ophthalmic Surg. Lasers Imaging
Effect of hyaluronic acid on intraocular pressure in rats
Invest. Ophthalmol. Vis. Sci.
Obstruction of aqueous outflow by sodium hyaluronate in enucleated human eyes
Am. J. Ophthalmol.
Animal models of glaucoma
Goldmann applanation tonometry in the conscious rat
Invest. Ophthalmol. Vis. Sci.
Quantitative analysis of retinal ganglion cell (RGC) loss in aging DAB/2NNia glaucomatous mice: comparison with RGC loss in aging C57/BL6 mice
Invest. Ophthalmol. Vis. Sci.
Cytoarchitecture of the retinal ganglion cells in the rat
Invest. Ophthalmol. Vis. Sci.
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