An electron microscopical study of epiplexus and supraependymal cells in the prenatal rat brain following a maternal injection of 6-aminonicotinamide.

Epiplexus and supraependymal cells in the lateral ventricles of both normal and experimental prenatal rats were studied with the scanning and transmission electron microscopes. In normal rats, the epiplexus cells, which were predominantly spindle shaped, displayed long filopodial processes inserted into the palisade of microvilli of the choroid epithelium; their cell bodies appeared relatively smooth with occasional blebs. In experimental animals in which the mother was given an injection of 6-aminonicotinamide (6-AN), the cell bodies of the epiplexus cells became extremely ruffled or blebbed. They were seen to be actively involved in the phagocytosis of leaked erythrocytes. The behaviour of supraependymal cells was rather similar. When stimulated by a 6-AN injection, the cells showed large prominent blebs and they too were engaged in phagocytic activity. It was concluded from this study that intraventricular macrophages bearing numerous filopodia are the less active cells whereas those bearing shorter processes, in particular, blebs or ruffles, represent the active form.