Effects of VEGF and Dll4/Notch pathways on blood vessel pruning/regression. (A-B) Eight-day-old pups were injected intravitreally with 4 μg of Fc control (A) or 4 μg of VEGF Trap (B), and retinas were analyzed 24 hours later (original magnifications, ×40). (C-F) Effects of Dll4-Fc and VEGF-A on persistent blood vessel density OIR. Eight-day-old pups were injected ITV with 4 μg of Dll4-Fc or 1 μg of VEGF-A. Animals were placed into high oxygen chamber 24 hours later and retinas harvested on P10. Total blood vessel length was measured per 40× microscopic field (F).