Figure 3.

Prolonged hyperoxia results in degeneration of photoreceptors in the posterior portion of the retina that is prevented by increased expression of FGF2 in photoreceptors. A section through the posterior retina of a FGF2 transgene-negative mouse (control) that was exposed to 75% oxygen for 2 weeks shows marked thinning of the outer nuclear layer (A), whereas the posterior outer nuclear layer of a transgene-positive mouse (Rho/FGF2) exposed to 75% oxygen for 2 weeks appears normal (C). In the periphery of the retina of a transgene-negative mouse the outer nuclear layer is normal (B), but becomes progressively thinner toward the posterior portion of the retina (right). In contrast, the retina of a transgene-positive mouse has a normal outer nuclear layer in the periphery that becomes thicker toward the posterior retina (D). There was no significant difference in outer nuclear thickness 100 μm from the optic nerve in transgene-negative mice (E) compared to transgene-positive mice (F) that were not exposed to 80% oxygen, or those exposed to 75% oxygen for 1 week (G versus H). But transgene-negative mice exposed to 75% oxygen for 2 weeks showed marked thinning of the outer nuclear layer (I) compared to transgene-positive mice exposed to 80% oxygen for 2 weeks (J).