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Frontiers of Medicine

ISSN 2095-0217

ISSN 2095-0225(Online)

CN 11-5983/R

Postal Subscription Code 80-967

2018 Impact Factor: 1.847

Front Med    2013, Vol. 7 Issue (3) : 367-377     DOI: 10.1007/s11684-013-0266-2
A modified chronic ocular hypertension rat model for retinal ganglion cell neuroprotection
Lichun Zhong()
Ocular Science Department, Toxikon Corporation, Bedford, MA 01730, USA
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This study aimed to modify a chronic ocular hypertension (OHT) rat model to screen for potential compounds to protect retinal ganglion cells (RGCs) from responding to increased intraocular pressure (IOP). A total of 266 rats were prepared and randomly grouped according to different time-points, namely, weeks 3, 8, 16, and 24. Rats were sedated and eye examination was performed to score as the corneal damage on a scale of 1 to 4. The OHT rat model was created via the injection of a hypertonic saline solution into the episcleral veins once weekly for two weeks. OHT was identified when the IOP at week 0 was≥6 mmHg than that at week -2 for the same eye. Viable RGCs were labeled by injecting 4% FluoroGold. Rats were sacrificed, and the eyes were enucleated and fixed. The fixed retinas were dissected to prepare flat whole-mounts. The viable RGCs were visualized and imaged. The IOP (meanβ±βSD) was calculated, and data were analyzed by the paired t-test and one-way ANOVA. The OHT model was created in 234 of 266 rats (87.97%), whereas 32 rats (12.03%) were removed from the study because of the absence of IOP elevation (11.28%) and/or corneal damage scores over 4 (0.75%). IOP was elevated by as much as 81.35% for 24 weeks. The average IOP was (16.68β±β0.98)βmmHg in non-OHT eyes (n = 234), but was (27.95±0.97)βmmHg in OHT eyes (n = 234). Viable RGCs in the OHT eyes were significantly decreased in a time-dependent manner by 29.41%, 38.24%, 55.32%, and 59.30% at weeks 3, 8, 16, and 24, respectively, as compared to viable RGCs in the non-OHT eyes (P<β0.05). The OHT model was successfully created in 88% of the rats. The IOP in the OHT eyes was elevated by approximately 81% for 24 weeks. The number of viable RGCs was decreased by 59% of the rats in a time-dependent manner. The modified OHT model may provide an effective and reliable method for screening drugs to protect RGCs from glaucoma.

Keywords chronic ocular hypertension      intraocular pressure      retinal ganglion cells      neuroprotection      glaucoma     
Corresponding Authors: Zhong Lichun,   
Issue Date: 05 September 2013
URL:     OR
IOP (mmHg) Rat strains/sex/agenTonometerSystemicanesthesiaReference
15.50±0.60Brown Norway, male retired breeder5GoldmannNo[25]
21.00±1.00Brown Norway17TonopenNo[26]
16.70±2.30Brown Norway132TonoLabNo[28]
25.10±0.50Brown Norway, adult14TonopenYes[29]
12.10±2.80Na?ve Brown Norway adult17TonopenYes[30]
28.10±0.50Na?ve Brown Norway adult20TonopenYes[31]
15.00±0.00Sprague-Dawley, male adult12PerkinsYes[33]
16.10±1.10Wistar, adult25TonopenYes[34]
16.10±0.40Wistar, male25TonopenYes[35]
17.40±1.30Wistar, male32TonopenYes[36]
12.20±3.60Wistar, male9TonopenYes[37]
14.85±0.65Wistar, male6TonopenYes[38]
18.40±0.10Wistar, male132TonoLabNo[39]
18.40±0.10Wistar, female10PneumotonometerYes[40]
14.40±0.30Brown Norway, male10TonoLabNo[41]
19.00±0.50Brown Norway8TonoLabYes[42]
17.80±2.34Sprague-Dawley, male6TonopenNo[43]
Tab.1  Summary of normal IOP (mean±SD) reported by different research groups
OHT model creationTotal266100.00
UsedSubtotal (IOP≥6 mmHg)23487.97
Corneal damage score≤34920.94
OHT eyesNon-OHT eyesTemporary cataracts4271717.952.997.26
Body weight loss114.70
Body weight gain22395.30
IOP&lt;6 mmHg3011.28
Corneal damage score≥420.75
Tab.2  Details of animals in the study
IOP measurementnon-OHT eyeOHT eye
Individual single measurement5 to 28 (n = 11 050)18 to 46 (n = 6 370)
Animal average (mean±SD)13.75±4.27 to 18.35±4.39 (n = 234)25.53±4.04 to 32.00±8.49 (n = 234)
Tab.3  Range of IOP measurements (mmHg)
Fig.1  Comparison of the elevated IOP in the OHT eyes after the hypertonic saline injection and the normal IOP in the non-OHT eyes.
Fig.2  Comparison of manual and automatic RGC counts. (A) Correlation of manual and automatic counts. (B) Total RGCs counted by both methods.
Fig.3  Loss of RGCs on OHT and non-OHT animals. Micrographs of RGCs (A) show the time dependence of the number of viable RGCs (B) and the % loss of RGCs (C).
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