Migration of neuroblasts through partial necrosis of the cerebral cortex in newborn rats-contribution to the problems of morphological development and developmental period of cerebral microgyria. Histological and autoradiographical study.

Abstract

Focal aseptic necrosis of the cerebral cortex was induced in newborn rats by focal contact freezing. In the region of freezing the following changes took place: necrosis of the pia mater, total necrosis of the differentiating Ist–IVth layers of the cortex and partial necrosis of the Vth and VIth layers of the cortex. The VIth-b layer was mostly preserved. In partial necrosis the differentiating neuroblasts died. The capillaries and migrating neuroblasts destined for the Ist, IInd, and IIIrd cortex layer survived. They stopped only at the periphery of total necrosis and continued to differentiate. After healing, an atypical cortex, consisting of four layers, was formed in the necrotic region, quite similar to the microgyric cortex of four layers known in the human. After deeper necrosis a cortical microsulcus developed, also formed by a cortex of four layers. The newly formed first microgyric (molecular) layer had its histologic structure homologous to the molecular layer of the surrounding cortex. The second microgyric layer (outer, cellular one) was formed by neuroblasts assigned to the IInd and IIIrd normal layers, which migrated through partial necrosis and took up their final position at the periphery of total necrosis. The third microgyric (light) layer was formed by the original Vth layer destroyed by partial necrosis, and it contained single neurons and glial cells. The fourth microgyric layer was formed by the persistent deep part of the VIth layer. The four layered cortex was formed only during the time of neuroblastic migration. The findings are discussed in relation to the normal pathogenesis of cortical microgyria in children. The experimental findings show that the microgyric cortex is formed only during the course of neuroblastic migration.