Experimental Glaucoma Induced by Ocular Injection of Magnetic Microspheres

Bunker, Shannon; Holeniewska, Joanna; Vijay, Sauparnika; Dahlmann‐Noor, Annegret; Khaw, PT; Ng, Y. Jack; Shima, David T.; Foxton, Richard

doi:10.3791/52400

Cited by 20 publications

(14 citation statements)

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“…In mice, a range of approaches have been used to chronically increase IOP over weeks to months. Studies have targeted episcleral venous outflow via cauterization (Ruiz-Ederra and Verkman, 2006 ), and laser ablation (Mabuchi et al, 2004 ; Holcombe et al, 2008 ), while intracameral injections (into the anterior chamber) of inert materials to impede trabecular outflow have also been undertaken (Benozzi et al, 2002 ; Moreno et al, 2005 ; Morrison et al, 2008 ; Sappington et al, 2009 ; Frankfort et al, 2013 ; Bunker et al, 2015 ). Such approaches often require more than a single manipulation to create a chronic mild IOP elevation that mimics the human condition of ocular hypertension (Cone et al, 2012 ).…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Circumlimbal Suture Model of Chronic IOP Elevation in Mice and Assessment of Changes in Gene Expression of Stretch Sensitive Channels

et al. 2017

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To consider whether a circumlimbal suture can be used to chronically elevate intraocular pressure (IOP) in mice and to assess its effect on retinal structure, function and gene expression of stretch sensitive channels. Anesthetized adult C57BL6/J mice had a circumlimbal suture (10/0) applied around the equator of one eye. In treated eyes (n = 23) the suture was left in place for 12 weeks whilst in sham control eyes the suture was removed at day two (n = 17). Contralateral eyes served as untreated controls. IOP was measured after surgery and once a week thereafter. After 12 weeks, electroretinography (ERG) was performed to assess photoreceptor, bipolar cell and retinal ganglion cell (RGC) function. Retinal structure was evaluated using optical coherence tomography. Retinae were processed for counts of ganglion cell density or for quantitative RT-PCR to quantify purinergic (P2x7, Adora3, Entpd1) or stretch sensitive channel (Panx1, Trpv4) gene expression. Immediately after suture application, IOP spiked to 33 ± 3 mmHg. After 1 day, IOP had recovered to 27 ± 3 mmHg. Between weeks 2 and 12, IOP remained elevated above baseline (control 14 ± 1 mmHg, ocular hypertensive 19 ± 1 mmHg). Suture removal at day 2 (Sham) restored IOP to baseline levels, where it remained through to week 12. ERG analysis showed that 12 weeks of IOP elevation reduced photoreceptor (−15 ± 4%), bipolar cell (−15 ± 4%) and ganglion cell responses (−19 ± 6%) compared to sham controls and respective contralateral eyes (untreated). The retinal nerve fiber layer was thinned in the presence of normal total retinal thickness. Ganglion cell density was reduced across all quadrants (superior −12 ± 5%; temporal, −7% ± 2%; inferior −9 ± 4%; nasal −8 ± 5%). Quantitative RT-PCR revealed a significant increase in Entpd1 gene expression (+11 ± 4%), whilst other genes were not significantly altered (P2x7, Adora3, Trpv4, Panx1). Our results show that circumlimbal ligation produces mild chronic ocular hypertension and retinal dysfunction in mice. Consistent with a sustained change to purinergic signaling we found an up-regulation of Entpd1.

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Section: Introductionmentioning

confidence: 99%

Characterization of the Circumlimbal Suture Model of Chronic IOP Elevation in Mice and Assessment of Changes in Gene Expression of Stretch Sensitive Channels

et al. 2017

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“…Rats used in this study had various degrees of optic nerve health. Each animal had one eye with experimental glaucoma induced unilaterally by either microbead injection (12 animals) [19][20][21] or hypertonic saline injection (2 animals) 22 . Optic nerves in the resulting dataset ranged from ostensibly normal to severely damaged due to ocular hypertension.…”

Section: Methodsmentioning

confidence: 99%

AxoNet: A deep learning-based tool to count retinal ganglion cell axons

Ritch

Hannon

Read

et al. 2020

Sci Rep

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in this work, we develop a robust, extensible tool to automatically and accurately count retinal ganglion cell axons in optic nerve (on) tissue images from various animal models of glaucoma. We adapted deep learning to regress pixelwise axon count density estimates, which were then integrated over the image area to determine axon counts. the tool, termed Axonet, was trained and evaluated using a dataset containing images of on regions randomly selected from whole cross sections of both control and damaged rat ons and manually annotated for axon count and location. this rat-trained network was then applied to a separate dataset of non-human primate (nHp) on images. Axonet was compared to two existing automated axon counting tools, AxonMaster and AxonJ, using both datasets. Axonet outperformed the existing tools on both the rat and nHp on datasets as judged by mean absolute error, R 2 values when regressing automated vs. manual counts, and Bland-Altman analysis. Axonet does not rely on hand-crafted image features for axon recognition and is robust to variations in the extent of on tissue damage, image quality, and species of mammal. therefore, Axonet is not speciesspecific and can be extended to quantify additional ON characteristics in glaucoma and potentially other neurodegenerative diseases. Glaucoma is the leading cause of irreversible blindness worldwide 1,2 , and thus is a significant research focus. This optic neuropathy is characterized by degeneration and loss of retinal ganglion cells (RGCs), which carry visual signals from the retina to the brain. Therefore, an important outcome measure in studying glaucomatous optic neuropathy, particularly in animal models of the disease, is the number and appearance of RGC axons comprising the optic nerve 3,4 , usually evaluated from images of optic nerve cross sections. Using images obtained by light microscopy is known to result in an axon count underestimation of around 30% relative to counts from images obtained by transmission electron microscopy 5,6. However, light microscopy is widely used to count optic nerve axons because of its lower cost and favorable time requirements for tissue preparation. Therefore, in this work we focus on axon counting in optic nerve images generated by light microscopy. Manual counting is the gold standard approach to quantify RGC axons, but it is extremely labor-intensive, since RGC axon numbers in healthy nerves range from the tens of thousands in mice to more than a million in humans 7. Further complicating axon quantification is the fact that axon appearance can be highly variable. For example, in the healthy nerve, most axons are characterized by a clear central axoplasmic core and a darker myelin sheath; following previous work 5,8 , we will refer to such an appearance as "normal". However, in damaged nerves (and even occasionally in ostensibly heathy nerves), other axon appearances occur, such as an incomplete myelin sheath and/or a darker axoplasmic region. Such variability further increases the time needed for axon counting,...

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“…A modification to the original technique involves using a toroidal‐shaped magnet to rapidly draw the beads to the iridocorneal angle (Bunker et al. ).…”

Section: Hypertensive Glaucoma Modelsmentioning

confidence: 99%

Review of rodent hypertensive glaucoma models

Biswas

Wan

2018

Acta Ophthalmologica

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Glaucoma is a neurodegenerative disease characterized by the progressive loss of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is a primary risk factor for the development and progression of glaucoma. Rodent models of glaucoma have greatly improved our understanding of the pathophysiology of glaucoma and served as a useful tool to investigate neuroprotective agents. An ideal glaucoma animal model should be easy to induce, reproducible, biologically plausible and predictable. Of the available animal models of glaucoma, rodents are commonly studied because they have a relatively short life span and can be genetically altered. A successful hypertensive glaucoma model should induce structural glaucomatous changes: including loss of retinal nerve fibres, retinal ganglion cells and optic-disc cupping along with IOP elevation. The level and duration of IOP elevation should be titratable depending on the targeted glaucomatous damage. This review summarizes the outcomes of induced rodent hypertensive glaucoma models including intracameral injection of microbeads, laser photocoagulation, episcleral vein cauterization, injection of hypertonic saline and hyaluronic acid. We aim to provide a detailed overview of each of the models with a focus on parameters that defines a successful glaucoma model. The induced IOP elevation and duration of elevation varied among the different models and strain of rodent; nonetheless, they all achieved a sustainable raised IOP with corresponding RGC loss. The limitations of each model are discussed.

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Experimental Glaucoma Induced by Ocular Injection of Magnetic Microspheres

Cited by 20 publications

References 10 publications

Characterization of the Circumlimbal Suture Model of Chronic IOP Elevation in Mice and Assessment of Changes in Gene Expression of Stretch Sensitive Channels

Characterization of the Circumlimbal Suture Model of Chronic IOP Elevation in Mice and Assessment of Changes in Gene Expression of Stretch Sensitive Channels

AxoNet: A deep learning-based tool to count retinal ganglion cell axons

Review of rodent hypertensive glaucoma models

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