Differences in wound healing pattern between mature and immature brain behavior of extravasated serum protein

To clarify the fate of extravasated serum protein and tissue reaction following blood brain-barrier breakdown in mature and immature brain, we produced cryogenic injury in the cortices of adult and post natal day 2 rats, and immunohistochemical examination with GFAP, vimentin and albumin, endogenous tracer of serum proteins, antibodies. Mature and immature brain showed the same histological changes by day 3. However, fibrotic scar, cyst formation and GFAP, vimentin-positive astrocytosis were main features in mature brain, fusion of adjoining cortical plate without scar and astrocytosis was typical in the immature brain. In adult rats, presence of albumin was observed near the lesion on day 1, evidently extending to the contralateral hemisphere on day 7 and localized again around scar and cyst on day 14. In the P2 rats, albumin was present in both hemispheres on day 1, but was localized to molecular layer periventricular region and choroid plexus on day 7. No albumin was detected on day 14. These results suggest that rapid spreading and clearance of extravasted serum proteins may take place in the immature brain and this may be deeply involved in the characteristic wound healing pattern.