Increased expression of OPN protein in the neonatal mouse brain after hypoxia-ischemia-induced brain injury. (A) through (H) Osteopontin (OPN)-positive staining (arrows in A and B) in the contralateral hemisphere (A and C) and ipsilateral hemisphere (B and D) at 6 hours after hypoxia-ischemia (HI)-induced injury. The positive staining was seen in the hippocampus, the lateral ventricle area (C and D), the thalamus and the meninges. (C) and (D) Enlarged images of the periventricular areas shown within the boxed areas in (A) and (B), (E) through (H) Higher-magnification images of OPN-positive cells from the periventricular region (E and F) and white matter (G and H) of the ipsilateral hemisphere. (I) through (M) At 3 days after HI, OPN-positive immunostaining was found mainly in the subcortical white matter area (arrows in I) in the ipsilateral hemisphere. (J) through (M) Higher-magnification images of OPN-positive cells in the ipsilateral hemisphere white matter (J), thalamus (K) and cortex (L and M). (N) through (P) The perinuclear expression of OPN (arrows) in the brain after HI. Green: OPN staining. Blue: nuclear staining. Bars inD = 50 μm; bars in E through H, J through M, and P = 10 μm; bars in N and O = 10 μm.