[Development of the fetal brain and lesion repair].

The process of lesion repair in the dramatically developing fetal brain shows a distinctive feature from that in the developed normal brain. The reason for the difference probably can be clarified by the anatomic features of the fetal brain. First, a wide extracellular space, which is necessary for the cell motility when a brain develops, preexists in the fetal brain. Secondly, it is also important that there are no cell-to-cell junctions in a fetal brain and each cell can freely locomote. Therefore, necrotized neuroblasts can be easily removed as they are "in the normal condition" by macrophages. As the astrocytes, which play an extremely important role in the developed adult brain for the repair of lesion, are still before gliogeneses or under differentiation in the fetal brain, there is little or no astrocytosis as compared with the developed brain. Therefore, the lesion repair process results in the production of a malformed brain.