Establishment of monocular-limited photoreceptor degeneration models in rabbits

Abstract

Background: Numerous rodent models of photoreceptor degeneration have been developed for the study of visual function. However, no viable model has been established in a species that is more closely related to Homo sapiens. Here, we present a rabbit model of monocular photoreceptor degeneration.

Methods: We tested 2 chemicals, verteporfin and sodium nitroprusside (SNP), for developing a 1-eye limited photoreceptor degeneration model in pigmented rabbits. After the intravenous injection of verteporfin, the retina was exposed to light from a halogen lamp for 0, 10, 30, or 60 min. Alternately, 100 μL of various concentrations of sodium nitroprusside (0.1 mM, 0.5 mM, and 1 mM) were intravitreously injected into the rabbit eye. Retinal degeneration was evaluated by fundus photography, electroretinogram (ERG), and histological examinations.

Results: Fundus photographs of animals in the verteporfin- or SNP-treated groups showed evidence of retinal degeneration. The severity of this degradation depended on the duration of light exposure and the concentration of SNP administered. The degeneration was clearly limited to the light-exposed areas in the verteporfin-treated groups. Extensive retinal atrophy was observed in the SNP-treated groups. The a- and b-wave amplitudes were dramatically decreased on the ERGs from SNP-treated groups. Histological examination revealed that either verteporfin or SNP induced severe photoreceptor degeneration. High-dose SNP treatment (1 mM) was also associated with inner retinal layer degeneration.

Conclusions: Both SNP and verteporfin clearly caused photoreceptor degeneration without any effect on the contralateral eye. These compounds therefore represent valuable tools for the empirical investigation of visual function recovery. The findings will inform guidelines for clinical applications such as retinal prostheses, cell-based therapy, and gene therapy.

Figure 1

Fundus photographs taken 2 weeks after treatment with PDT or intravitreal SNP. The control fundus is shown in A. PDT was performed with 0.5 mg/kg verteporfin and a halogen reflector lamp for 0 (B), 10 (C), 30 (D), or 60 (E) min. One hundred microliters of SNP (F: 0.1 mM, G: 0.5 mM, H: 1 mM) was injected intravitreously into a rabbit eye. Arrows and arrowheads indicate the pigmentation and the area of severe degeneration, respectively. Lesions are clearly demarcated by a broken line.

Figure 2

The typical waveforms of electroretinogram (ERG) responses evoked by a white flash (duration: 10 ms; light intensity: 10, 100, and 1000 lux, top to bottom). Waveforms with no treatment are shown in A. Eyes were submitted to PDT with light exposure (B: 10 min, C: 30 min, D: 60 min) or SNP injection (E: 0.1 mM, F: 0.5 mM, G: 1 mM). Comparison of b-wave amplitudes in eyes treated with either verteporfin or SNP (H). Data are shown as mean ± S.D., n = 3, *, #, $; p < 0.05, **, ##, $$; p < 0.01, unpaired t-test.

Figure 3

Histological evaluations of photoreceptor degeneration after either PDT treatment or SNP injection. Retinal histology without treatment is shown in (A). PDT was performed with 0.5 mg/kg verteporfin and a halogen reflector lamp for 0 (B), 10 (C), 30 (D), or 60 (E, F) min. The bar in the figure (F) indicates the area exposed to light. One hundred microlitters of SNP (G: 0.1 mM, H: 0.5 mM, I: 1 mM) are injected intravitreously injected into a rabbit eye.