Effects And Mechanisms Of Dexamethasone On Photic Injury In Rat Retinal

PURPOSE: In the current study ,the effect of dexamethasone on light -induced apoptosis and the mechanisms of it on prevention photic-injury in rat retinal was determined.METHOD: Retina cell apoptosis was induced in retina of adult Wister rats by exposure to operating microscope light (diffuse white light ). Dexamethasone sodium phosphate(52mg/kg) was applied in a single intraperitoneal injection at the time that before 1hour light exposure. Control animal received an equal volume of physiological saline solution .Wistar rats were exposed to diffused white light (12000lux) for 1 hour ,allowed to recover in the dark ,and euthanatized at 0, 2, 6, 12, 24 or 48 hours after light exposure . Nicked DNA was examed by in situ TdT-dUTP terminal nick -end labeling (TUNEL) and c-FOS ,Caspase-1 were detected immunohistochemically . The total number of positive nuclei per retina section was counted manually under a Diaster Leica microscope .The lengthof the outer nuclear layer (ONL) and Inner nuclear layer (INL) was recorded by an image analyzing system. The data was analyzed statistically with SAS8.0 software.RESULT: â‘ There were TUNEL-positive-nuclei both in ONL and INL, which were a time -dependent change .After light exposure , there was a gradual increase in the number of TUNEL-positive nuclei in the ONL and INL from 0 to 24 hour and dropped at 48 hours. â‘¡ There was significant difference of morphometry on TUNEL-positive-nuclei in rat retina between experimental group and control group at the same time after photic injury. â‘¢ Immunohistochemical staining of c-FOS showed: there was also a gradual increase in the number of c-FOS-positive nuclei in the INL from 0 to 24 hours ,but immunoreaction of c-FOS in ONL was unremarkable, which indicate that dexamethasone could inhibit the expression of c-FOS in INL of rat retina after light expoure.â‘£ Immunohistochemical staining of Caspase-1 showed: accummlation of Caspase-1 was observed in the cytoplasm of photoreceptor in ONL and INL, there was gradual increase in the number of Caspase-1-positive nuclei in the ONL from 0 to 12 hours and dropped at 24 hours, which indicated that dexamethasone could inhibit the expression of Caspase-1 in ONL,but not in INL.CONCLUSION: The methods that we used at this study can successfully obtained animal model of photic injury for research aim. Dexamethasone furthermore preserve retina function by preventing retina cells from apoptosis. The effect of dexamethasone decrease retina cells apoptosis may relate to downregulation of the expression of c-FOS and caspase-1.