Effects of oxygen and bFGF on the vulnerability of photoreceptors to lightdamage

PURPOSE. TO test whether tissue oxygen levels affect the vulnerability of p hotoreceptors to damage by bright continuous light (BCL). METHODs. Albino rats were raised in standard conditions of cyclic light (12 -hour light, 12-hour darkness) with the light level at 5 to 10 lux or 40 to 65 lux. They were then exposed to BCL (1000-1400 lux), either continuously for 48 hours or for the day or night components of the 48-hour period. Dur ing BCL, some rats were kept in room air (normoxia, 21% oxygen), some in hy poxia (10%), and some in hyperoxia (70%). Their retinas were examined for c ell death, for the expression of basic fibroblast growth factor (bFGF), and for response to light (electroretinogram, ERG). RESULTS. The death of retinal cells induced by BCL was confined to photorec eptors. Within the retina, the severity of death was inversely related to t he level of bFGF immunolabeling in the somas of the outer nuclear layer (ON L) before exposure. The death of photoreceptors was accompanied by an upreg ulation of bFGF protein levels in the ONL and by a decline in the ERG. Both hypoxia and hyperoxia during BCL reduced the photoreceptor death, bFGF upr egulation, and ERG decline caused by BCL. The protective effects of hyperox ia and hypoxia were evident during both the day and night halves of the dai ly cycle. Hypoxia or hyperoxia alone did not upregulate bFGF or ciliary neu rotrophic factor (CNTF) expression in the retina. CONCLUSIONS. Photoreceptors are protected from light damage by hypoxia and hyperoxia during exposure. The protection provided by oxygen levels operate s during both day and night. The protection is not mediated by an upregulat ion of bFGF or CNTF.