Abstract
The aim of this article was to explore the mechanism of injury in rat retina after constant low-level helium-neon (He-Ne) laser exposure and therapeutic effects of MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist, on laser-induced retinal injury. He-Ne laser lesions were created in the central retina of adult Wistar Kyoto rats and were followed immediately by intraperitoneal injection of MK-801 (2 mg/kg) or saline, macroscopical and microscopical lesion were observed by funduscope and light microscope. Ultrastructural changes of the degenerating cells were examined by electron microscopy. Photoreceptor apoptosis was evaluated by TdT-mediated dUTP nick end-labeling (TUNEL). mRNA levels were measured by in situ hybridization and NMDA receptor expression was determined by immunohistochemistry. Laser induced damage was histologically quantified by image-analysis morphometry. Electroretinograms (ERGs) were recorded at different time point after the cessation of exposure to constant irradiation. There was no visible bleeding, exudation or necrosis under funduscope. TUNEL and electron microscopy showed photoreceptor apoptosis after irradiation. MK-801-treated animals had significantly fewer TUNEL-positive cells in the photoreceptors than saline-treated animals after exposure to laser. In situ hybridization (ISH) showed that the NMDAR mRNA level of MK-801-treated rats decreased in the inner plexiform layer 6 h after the cessation of exposure to constant irradiation when compared with that of saline-treated rats. So did Immunohistochemistry (IHC). Electroretinogram showed that b-wave amplitudes of MK-801-treated group were higher than that of saline-treated group after laser exposure. These findings suggest that Low level laser may cause the retinal pathological changes under given conditions. High expression of NMDAR is one of the possible mechanisms causing experimental retinal laser injury of rats. MK-801 exhibits the therapeutic effect due to promote the recovery of structure and function of injured retina.
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