Resistance of photoreceptors in the C57BL/6-c^2J, C57BL/6J, and BALB/cJ mouse strains to oxygen stress: Evidence of an oxygen phenotype

Purpose. To assess the vulnerability of retinal photoreceptors in the BALB/cJ, C57BL/6J, and C57BL/6-c^2J (c2J) mouse strains to hypoxic and hyperoxic stress. Methods. Mice were raised in dim cyclic light. Pups aged postnatal day 7 (P7) were exposed to hypoxia (11-12% oxygen) for periods up to 23 days. Adult mice were exposed to either hypoxia (12% oxygen) or to hyperoxia (75% oxygen) for up to 2 weeks. Using the TUNEL (terminal dUTP-mediated nick end labeling) technique retinas were examined for cell death. Results. In juvenile mice, hypoxia induced a robust increase in photoreceptor death in the C57BL/6J strain and a weaker increase in the C57BL/6-c^2J strains. In the adult, hypoxia was associated with a small reduction in photoreceptor death in the C57BL/6-c^2J strains. Hyperoxia caused substantial photoreceptor death in both the C57BL/6-c^2J and C57BL/6J strains. The BALB/cJ strain was more resistant to oxygen stress than the C57BL strains. Conclusions. The difference in oxygen vulnerability between C57BL/6J and BALB/c strains may provide a useful starting point for the analysis of genetic regulation of this vulnerability. The resistance of the C57BL/6-c^2J substrains to hypoxia may reflect their degenerative status.