Pre-exposure to low-power diode laser irradiation promotes cytoprotection in the rat retina

The aim of this study was to investigate whether pre-exposure to low-power laser irradiation can provoke an effect on cellular protection in the rat retina. The right eyes of 40 rats were exposed to a 3-mm diode laser beam for 1 min in different light intensities and different experimental sets: group A low power of 60 mW (34.27 J/cm² on the retina in consideration of the energy losses along the optical pathway) prior to high power of 80 mW (44.88 J/cm² on the retina in consideration of the energy losses along the optical pathway), group B high power, group C low power, group D (the left eyes from the counterpart of group A) and group E (untreated rat eyes) as controls. Morphological retinal change retinas were assessed using light microscopy and/or transmission electron microscopy. Heat shock protein (Hsp) 70 and cleaved caspase 3 protein expression were analyzed by immunohistochemical staining and Western blot. Cellular injury was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay. Hsp 70 expression in the inner plexiform layer and the outer plexiform layer in group A were 73.09 ± 6.49 and 78.03 ± 3.05 %, respectively, which was significantly higher (P < 0.05) than those observed in group B (59.07 ± 1.40 and 32.25 ± 4.26 %, respectively). The Hsp70/β-actin ratio was 0.49 ± 0.06 in group C, which was significantly higher (P < 0.05) than that of group B (0.27 ± 0.04). Cleaved caspase 3 expression in group C both was significantly lower than that observed in group B. TUNEL staining showed that positive cells in the outer nuclear layer and inner nuclear layer in group A were significantly lower than those of group B. Pre-exposure to a 60-mW (34.27 J/cm² on the retina) power laser irradiation stimulates a hyperexpression of Hsp70 together with a hypoexpression of cleaved caspase 3 in rat retina, which may suggest a cellular protective effect.