Immunocytochemical localization of alpha-fetoprotein in the developing rat brain.

The immunocytochemical localization of the alpha-fetoprotein (AFP), serum albumin (ALB), transferrin (Tf) and immunoglobulins (IgG) in developing rat brain has been studied by the indirect peroxidase technique using rabbit antibodies to AFP, ALB, Tf and IgG followed by goat anti-rabbit immunoglobulins conjugated with peroxidase. Evidence of a high selective staining for AFP and ALB is presented. The pattern of morphological localization of both proteins was similar throughout fetal and post-natal development up to 20-25 days of age. Large areas and groups of cells in all regions of the brain from the olfactory bulb to the medulla oblongata appeared positively stained at a given moment in the development. The labeling was cytoplasmic and, in the neuronal elements, extended to their axonic and dentritic prolongations. The intracellular localization of AFP and ALB in the developing rat brain may be related to the binding affinity of these proteins for oestrogens and/or essential fatty acids. The morphological data presented here suggest that both proteins are actively involved in the uptake of such substances by the cellular structures of the brain.