Intracellular alpha-fetoprotein and albumin in the developing nervous system of the baboon

The intracellular presence of alpha-fetoprotein (AFP) and of albumin in the brain and other neural derivatives of three Baboon fetuses (9,13 and 17 weeks of gestational age, respectively), was demonstrated by immunocytochemical techniques. The largest localization of both proteins was observed in the 9 week old fetus, where most neural tube and neural crest derivatives showed intracytoplasmic labelling. The staining decreased abruptly in the 17 week old fetus. In the brain, of the youngest fetus examined, the penetration of AFP and albumin into the cerebral wall is transependymal. The route seems to possess differential activity since IgG molecules never appeared internalized in spite of their presence, like AFP and albumin, in the choroid plexus and the ventricular spaces of this fetus. It is also worth noting that the labelling declines as myelination and glial cell development progress. The wide distribution of AFP and albumin labelling supports the conclusion that the intracellular uptake of these proteins is probably general in immature nervous structures. Attention is brought to the binding and transport of polyunsaturated fatty acids by AFP and albumin as a possible explanation for the transitory presence of these proteins in the developing nervous system.