Endogenous OPN Expression. (A) Endogenous OPN expression in the normal rat brain at age of day 0, 4, 7, 11, 14, and 21. The level of OPN was significantly decreased during development (*P<0.05, vs. day 0). N=4 in each time point. (B) Endogenous OPN expression in the brain was significantly increased and peaked at 48h following HI injury (*P<0.001, vs. contralateral hemisphere). N= 4 in each time point.