An Immunohistochemical Study of the Germinal Layer in the Late Gestation Human Fetal Brain

In the cerebral lateral ventricle of the human fetus, the embryonic ventricular and subventricular zones (VZ and SVZ) persist into the latter half of gestation, particularly in the lateral wall. The SVZ is usually referred to as the germinal layer at this stage. The VZ is gradually replaced by ependyma, a single epithelial layer composed of tanycytes and ciliated columnar cells. In the prematurely born infant, the germinal layer is frequently the site of haemorrhage, the incidence of which diminishes with increasing maturity. There are many contributory pathogenetic factors but the structure of the germinal layer itself is considered important. It contains numerous, thin walled vessels in a cellular matrix which demonstrates little fibrillary background. Immunohistochemical evidence of glial differentiation in the germinal layer was sought in 21 preterm brains, using antibody to glial fibrillary acidic protein (GFAP). Early immunoreactivity was due to GFAP positive tanycyte fibres. Subsequently, associated with astrocyte differentiation, there was progressive development of a glial fibre network. It is suggested that the increase in glial fibres may be a significant factor in capillary stabilization, and in the inverse relationship between gestation of the infant and the risk of intracerebral haemorrhage. The possible structural significance of the tanycyte is also highlighted.