Name: glaucoma-inducing procedure in an in vivo rat model and whole-mount retina preparation
Uploaded: 2016-03-12T14:00:00
Description: Watch this Scientific Journal Video about Glaucoma-inducing Procedure in an In Vivo Rat Model and Whole-mount Retina Preparation at JoVE.com

C. Linn is supported by an NIH grant (NIH NEI EY022795).

All procedures using animal subjects have been in accordance with the standards of the Institute of Animal Care and Use Committee (IACUC) at Western Michigan University.
1. Animals
<ol>
	<li>Use male and female rats 3 months of age in this study.</li>
	<li>Keep animals in a 12 hr light/dark cycle with free access to food and water.</li>
</ol>
2. Preparation of KAX Cocktail for Animal Anesthesia
<ol>
	<li>Dissolve 50 mg of xylazine (20 mg/ml) in 5 ml ketamine (100 mg...

This protocol describes a method of inducing glaucoma-like conditions in an in vivo rat model. This procedure uses an injection of hypertonic saline to induce scarring in the trabecular meshwork 29, 32. Developing scar tissue occludes the outflow of aqueous humor which increases pressure in the anterior chamber. With decreased outflow and pressure build up, the lens suspended by elastic ligaments pushes back into the vitreous chamber. Vitreous humor then applies pressure onto the retina damaging the f...

Glaucoma is a group of eye diseases affecting neurons in the retina, specifically, the retinal ganglion cells1-2. The axons of these cells converge to become the optic nerve carrying visual information to the brain where vision is perceived. Damage to RGCs and their axons therefore causes visual defects.
The primary characteristics associated with glaucoma disorders are RGC degeneration and death, increased intraocular pressure (IOP), and optic disk cupping and atrophy. These features lead to visual field loss or complete, irreversible blindness. Currently, glaucoma has caused blindness in 70 million people worldwide 3. As such, it is the world&#39;s third largest cause of blindness 4.
The exact mechanism of RGC death in glaucoma remains unknown. Much research has been done to unlock the mystery. It is known, however, that the primary risk factor of glaucoma is an increase in intraocular pressure due to irregular circulation of aqueous humor (AH) in the anterior chamber of the eye. AH acts as a transparent and colorless replacement for blood in the avascular anterior chamber of the eye. It nourishes the surrounding cells, removes secreted waste products from metabolic processes, transports neurotransmitters, and permits the circulation of drugs and inflammatory cells within the eye during pathological states 1.
The maintenance of aqueous humor circulation involves the ciliary body and the trabecular meshwork. Aqueous humor is produced by the ciliary body. It then flows into the anterior chamber to maintain the overall health of the ocular tissue. 75 - 80% of aqueous humor outflow is actively secreted through non-pigmentary ciliary epithelium when the fluid is filtered through three layers of spongy tissue in the ciliary muscle. The fluid exits through the trabecular meshwork and through Schlemm&#39;s Canal which empties into the blood system 5.The remaining 20 - 25% of outflow bypasses the trabecular meshwork and is passively secreted by ultrafiltration and diffusion through the uveo-scleral pathway. This pathway appears to be relatively independent of intraocular pressure 1.
When aqueous humor production and outflow are out of balance, pressure builds within the eye. As stated, this increase in intraocular pressure is the primary risk factor in the development of glaucoma. Such pressure causes damage to the intricate layers of neurons in the retina at the back of the eye. Damage to the retinal ganglion cell axons of the optic nerve causes the brain to no longer receive accurate visual information. As a result, the perception of vision is lost and complete blindness can occur.
To date, there is no cure for glaucoma. Different treatment methods exist that primarily aim to reduce intraocular pressure. These include topical medication classes such as beta1-adrenergic receptor blockers, or topical prostaglandin analogues. Beta blockers reduce the intraocular pressure by decreasing the production of aqueous humor 7. Prostaglandins function to reduce IOP by increasing the outflow of aqueous humor 8-14. Alpha adrenergic agonists and carbonic anhydrase inhibitors are also used as secondary methods of treatment. Alpha adrenergic agonists increase outflow through the uveoscleral pathway 15-17. Carbonic anhydrase inhibitors reduce the production of AH by enzymatic inhibition 18. Much more invasive procedures are also being used to treat glaucoma. Laser trabeculoplasty is used to increase the outflow of aqueous humor 19. Another surgical therapy, called trabeculectomy, creates an alternative drainage site to filter AH when the traditional trabecular pathway is blocked 20-21.
These treatment options have been known to effectively reduce IOP. However, up to 40% of glaucoma patients show normal IOP levels indicating a need for more complete therapeutic methods.22,23 Additionally, retinal ganglion cell death seen in glaucoma is irreversible once it begins and current treatments do not stop the progression of the disease 24-28. This has highlighted the need for effective neuroprotective therapies that target the survival of the neurons themselves. Development of glaucoma models is crucial for this development.
In this study we are demonstrating a method of inducing glaucoma-like effects in adult Long Evans rats using a modified procedure originally outlined by Morrison29. In this procedure, injections of 2 M hypertonic saline into the episcleral venous plexus induces glaucoma-like conditions by scarring tissue to reduce aqueous humor outflow in the trabecular meshwork leading to an increase in intraocular pressure and a significant loss of RGCs within one month of the procedure 30-31. Glaucoma-inducing procedures, such as the one described here, may be the key to unlocking new developments in glaucoma treatments.

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glaucoma-inducing procedure in an in vivo rat model and whole-mount retina preparation

Glaucoma is a disease of the central nervous system affecting retinal ganglion cells (RGCs). RGC axons making up the optic nerve carry visual input to the brain for visual perception. Damage to RGCs and their axons leads to vision loss and/or blindness. Although the specific cause of glaucoma is unknown, the primary risk factor for the disease is an elevated intraocular pressure. Glaucoma-inducing procedures in animal models are a valuable tool to researchers studying the mechanism of RGC death. Such information can lead to the development of effective neuroprotective treatments that could aid in the prevention of vision loss. The protocol in this paper describes a method of inducing glaucoma - like conditions in an in vivo rat model where 50 &#181;l of 2 M hypertonic saline is injected into the episcleral venous plexus. Blanching of the vessels indicates successful injection. This procedure causes loss of RGCs to simulate glaucoma. One month following injection, animals are sacrificed and eyes are removed. Next, the cornea, lens, and vitreous are removed to make an eyecup. The retina is then peeled from the back of the eye and pinned onto sylgard dishes using cactus needles. At this point, neurons in the retina can be stained for analysis. Results from this lab show that approximately 25% of RGCs are lost within one month of the procedure when compared to internal controls. This procedure allows for quantitative analysis of retinal ganglion cell death in an in vivo rat glaucoma model.

This section illustrates the apparatus components and procedure used to induce glaucoma-like conditions in an in vivo rat glaucoma model. We show the individual tools and equipment used to perform a hypertonic saline injection which causes an increase in intraocular pressure. We show the injection into the episcleral venous plexus with its characteristic blanching effect and the cloudy appearance of the anterior chamber that results. We also describe the process of retina removal...

Watch this Scientific Journal Video about Glaucoma-inducing Procedure in an In Vivo Rat Model and Whole-mount Retina Preparation at JoVE.com

Glaucoma-inducing Procedure in an In Vivo Rat Model and Whole-mount Retina Preparation

Glaucoma is characterized by damage to retinal ganglion cells. Inducing glaucoma in animal models can provide insight into the study of this disease. Here, we outline a procedure that induces loss of RGCs in an in vivo rat model and demonstrates the preparation of whole-mount retinas for analysis.

Glaucoma-inducing Procedure in an In Vivo Rat Model and Whole-mount Retina Preparation

Glaucoma is a disease of the central nervous system affecting retinal ganglion cells (RGCs). RGC axons making up the optic nerve carry visual input to the ...

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