Repair and reconstruction of the cortical plate following closed cryogenic injury to the neonatal rat cerebrum.

A cryogenic lesion was induced in the parietal cortex of neonatal rats at postnatal day 2, and the chronological sequence of cellular events during repair and reconstruction of the cortical plate examined. Serial sections of cerebra obtained at varying intervals ranging from 1 to 60 days postinjury were studied by light and electron microscopy and by immunocytochemistry for fibronectin, laminin, type IV collagen, vimentin and glial fibrillary acidic protein. In addition, localization of heavily labeled neurons (generated on embryonic day 20) in the cerebral cortical plate was examined by [3H]thymidine radioautography. Repair of a well-defined coagulative lesion was accomplished with little or no mesenchymal cell proliferation in either the necrotic zone or the leptomeninges. Eventually, fusion of the adjacent cortical plates took place with the formation of a microsulcus. Migration of neurons continued to take place along the outer margins of the lesion, and postmigratory neurons accumulated within the upper cortical layers. Around the microsulcus, heavily labeled neurons aligned themselves with layers II-III of the adjacent normal cortical plate. Irregular clusters of neurons closely abutting the leptomeningeal surface were frequently noted when repair took place without an intervening molecular layer and/or a well-defined pial-glial barrier. Supplementing intrinsic information inherent in migrating neurons, local environmental signals provided by the radial glia, glia limitans, basal lamina and pial-glial barrier appear to influence the polarity and final positioning of postmigratory neurons within the cortical plate. The necrotic zone within the deeper layers of the cortex eventually healed with a cell-sparse gliotic layer. The end result was a histological pattern that, in many respects, resembled that of human micropolygyria.(ABSTRACT TRUNCATED AT 250 WORDS)