Glial and neuronal differentiation in the human fetal brain 9-23 weeks of gestation

Nineteen human fetal brains ranging from 9-23 weeks of gestation were examined immunocytochemically for evidence of glial and neuronal differentiation. Radial glia were positive for vimentin and glial fibrillary acidic protein (GFAP) throughout the age range. S100-positive cells which were presumed to be astrocytes were present from 9 weeks; they were always more widespread in the cerebrum and the brainstem than GFAP-positive mature astrocytes, which could be detected with certainty only at 14 weeks. Carbonic anhydrase II (CA II)-positive oligodendrocytes were present in the brainstem in small numbers from 17 weeks. Neuronal fibre tracts in the cerebrum were positive for 160 kD phosphorylated neurofilament protein (BF10) from 9 weeks, but negative for 200 kD phosphorylated neurofilament protein (RT97) and for 70 and 200 kD non-phosphorylated neurofilament protein (NFP) whereas most tracts in the brainstem were positive for BF10 from 9 weeks and positive for the other neurofilament proteins from 14 weeks. Corticospinal tracts differed in remaining negative for neurofilament proteins other than BF10, which showed positive reaction throughout. Perikarya of differentiated neurons in all areas of the brain were neurofilament-negative but neuron specific enolase (NSE)-positive. Germinal eminence cells were focally vimentin-positive from 15 weeks, focally GFAP-positive from 17 weeks, and negative for all NFP and for NSE. The value of a short fixation time and pretreatment with trypsin in the immunocytochemical demonstration of GFAP is stressed.