Abstract
We have investigated the effects of light-emitting diode (LED)-induced phototoxicity (LIP) on cone-photoreceptors and their protection with brimonidine (BMD), brain-derived neurotrophic factor (BDNF), pigment epithelium-derived factor (PEDF), ciliary neurotrophic factor (CNTF) or basic fibroblast growth factor (bFGF). In anesthetized, dark adapted, adult albino rats a blue (400 nm) LED was placed perpendicular to the cornea (10 sec, 200 lux) and the effects were investigated using Spectral Domain Optical Coherence Tomography (SD-OCT) and/or analysing the retina in oriented cross-sections or wholemounts immune-labelled for L- and S-opsin and counterstained with the nuclear stain DAPI. The effects of topical BMD (1%) or, intravitreally injected BDNF (5 µg), PEDF (2 µg), CNTF (0.4 µg) or bFGF (1 µg) after LIP were examined on wholemounts at 7 days. SD-OCT showed damage in a circular region of the superotemporal retina, whose diameter varied from 1,842.4±84.5 µm (at 24 hours) to 1,407.7±52.8 µm (at 7 days). This region had a progressive thickness diminution from 183.4±5 µm (at 12 h) to 114.6±6 µm (at 7 d). Oriented cross-sections showed within the light-damaged region of the retina massive loss of rods and cone-photoreceptors. Wholemounts documented a circular region containing lower numbers of L- and S-cones. Within a circular area (1 mm or 1.3 mm radius, respectively) in the left and in its corresponding region of the contralateral-fellow-retina, total L- or S-cones were 7,118±842 or 661±125 for the LED exposed retinas (n = 7) and 14,040±1,860 or 2,255±193 for the fellow retinas (n = 7), respectively. BMD, BDNF, PEDF and bFGF but not CNTF showed significant neuroprotective effects on L- or S-cones. We conclude that LIP results in rod and cone-photoreceptor loss, and is a reliable, quantifiable model to study cone-photoreceptor degeneration. Intravitreal BDNF, PEDF or bFGF, or topical BMD afford significant cone neuroprotection in this model.
Highlights
In mammals nigthtlight vision is carried out by rod-photoreceptors, while cone-photoreceptors are responsible for daylight vision and colour discrimination
Quantitative analysis indicates that the thinning was mainly due to thickness diminution of the outer nuclear (ONL) and outer segment layers (OSL) of the retina (Fig. 4)
In the present study we have characterized for the first time, in vivo with Spectral Domain Optical Coherence Tomography (SD-Optic coherence tomography (OCT)) as well as ex vivo with fluorescence microscopy, the effects of a small phototoxic retinal lesion on the survival of L- and S-cones in the adult albino rat retina
Summary
In mammals nigthtlight (scotopic) vision is carried out by rod-photoreceptors, while cone-photoreceptors are responsible for daylight (photopic) vision and colour discrimination. Photopic vision is achieved by two types of cones, each carrying an opsin responsible for detection of short (Scones) and medium to long (L-cones) wave lengths, respectively. S-cones express the ultraviolet sensitive or SWS1 opsin and L-cones express the LWS opsin which detects green light and is referred as the L-opsin. The rat retina does not have a proper macula, it has a visual streak with highest concentrations of RGCs and L-cones, but mostly devoid of Scones, in an horizontal region along the dorsal retina [1, 2, 4,5,6]
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