| [Objective] To investigate the damage mechanism and the way to prevent and treat photic injury, by studying the regularity of expressive changes of rat retinal tumor necrosis factor(TNF) -α, and by studying the influence on the expression of TNF-αfrom pretreatment of Minocycline(MC).[ Methods] Fifty-four Sprague-Dawley(SD) rats,were divided into 3 groups randomly: MC-pretreated groups, PBS-pretreated groups and normal controls. The former two were further divided into four groups: 6h,3d,7d and 14d after photic in jury,randomly and respectively. There were 6 rats (12 eyes) in each group.All rats(including the normal controls) were given dark adaptation for 24h. The eyes were enucleated for the normal controls,and the others were given light exposure (caused by green fluorescent light) of 36h at 1737.9±393.0lux. MC or equal PBS were administrated to rats(45mg/kg) by intragastric administration 90 minutes before light exposure. The eyes were enucleated as arranged. The left eyes were embedded in paraffin, hematoxylin-eosin staining, TNF-αimmunohistochemistry staining, and the outer nuclear layer (ONL) thinkness were analyzed and measured using Image-Pro Plus. The right whole retinas were taken out immediately, homogenated and then the supernatant were chosen to be examined by enzyme-linked immunosorbent assay (ELISA). Statistical analysis was performed on SPSS 15.0 for windows.[ Results ] The outer retina was pathologically damaged from 6h after light exposure,and was most significantly damaged 7d after photic injury.The outer retina seemed much less damaged in the MC-pretreated groups compared to the PBS-pretreated groups by the section observations and by the measurement of ONL thickness. The ONL thickness comparison of the same stage between MC-pretreated groups and PBS-pretreated groups was statistically different (P<0.05).There was little TNF-αexpressed in the normal retina,with negative staining in immunohistochemistry(IHC) staining,and 38.75±7.83 pg/ml while examined with ELISA.There was an increase in both IHE staining and ELISA measurement 6h after light exposure in the PBS pretreated groups, and increased significantly when 3d. The expression decreased at 7d and 14d gradually. The expression of TNF-αshowed the similar changes in the MC-pretreated groups, but much less expression in every same stage compared with that of the PBS-pretreated groups, with statistical differences in the same stages(P<0.05). The TNF-αexpression of every stage in both the MC-pretreated groups (except the 14d group,which has no statistical difference with that of the normal group ) and the PBS-pretreated groups statistically differed from that of the normal group(P<0.05).[ Conclusion ] This experiment studied the expressive changes of rat retinal tumor TNF-α, and the influence from pretreatment of MC for the first time,and drew the following conclusion: the retinal TNF-αexpression increased after photic injury and gave dynamic changes, with a close relationship with the degree of retinal photic injury, which showed that the overdose TNF-αexpression in rat retina caused and aggravated the retinal damage. Minocycline can give protection to the photoreceptors, with the possible main mechanism of inhibiting the activation of the cells that could produce TNF-αand then reduced the oversecretion of TNF-α. Microglial cells which could produce TNF-αalso involved in the pathophysiological process of retinal photic injury.
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