The behavior of the extracellular matrix and the basal lamina during the repair of cryogenic injury in the adult rat cerebral cortex.

A well-defined coagulative lesion was produced in the fronto-parietal cortex of adult rats by application of a cold probe, and the chronological sequence of events during the healing process, particularly the relationship between astroglial processes and the newly forming basal lamina (BL) and the behavior of the extracellular matrix (ECM) was examined immunocytochemically and ultrastructurally. By electron microscopy, new BL synthesis was first noted 7 days following injury, and a continuous and well-defined BL was present from 14 days onward. These findings correlated well with the pattern of immunoreactivity for laminin and for type IV collagen. Both laminin and type IV collagen appeared both to be produced primarily by mesenchymal cells within and around the wound as well as those of the blood vessels, and to become an integral part of the new BL. Although there was no immunocytochemical evidence to indicate secretion of laminin, type IV collagen or fibronectin by astrocytes, a well-defined BL appeared to form only in tight apposition with astroglial processes over the pial surface. This suggests that the BL is formed by subpial astrocytes in close interaction with ECM components at the pial surface. Fibronectin appears to contribute significantly to the formation of the BL by providing a suitable substratum for the coordinated cellular interaction necessary for successful regeneration of the BL.