Early appearance of type II astrocytes in developing human fetal brain.

To compare rat and human glial development, we examined the cellular composition of human fetal brain in short-term cultures and fresh cell suspensions from fetal ages ranging from 7 to 16 weeks, utilizing the cell type-specific markers which define glial subsets in rats. Here we report that unlike the early rat central nervous system (CNS), 7-10 week human fetal brain contains mostly astrocytes that can be characterized as type II rather than type I. Type I astrocytes become more prevalent in 16-week gestational age human brain. Although cells morphologically and immunocytochemically similar to the rat 02-A cell are found in human fetal brain and spinal cord, these cells were not induced to express galactocerebroside in serum-free media and did not have vimentin-containing intermediate filaments as do rat 02-A cells. These results suggest that functional differences may exist between rat type I and type II astrocytes and phenotypically similar cells found in humans.