THE SURFACE AREA OF CHOROID PLEXUS IN NORMAL MOUSE EMBRYOS

Abstract

To estimate the total surface area of the choroid plexus and the relative size of its various regions in embryonic life, measurements were made on 30 normal mouse embryos, the stage of development being indicated by brain volume. In addition, in 22 of the embryos, the ependyma wall area was measured to establish the relationship in size with the developing plexus. Serial sections of the embryo heads were cut, and every 10th projected on to paper, after which the surface of the choroid plexus and the ependyma in all ventricles was drawn and measured. The measurements were carried out either with a curvimeter or by measuring a thin fixed to the outline. Brain volume was determined by drawing the outline of the brain and measuring the area of the figure with a planimeter. With increasing brain volume both the total choroid plexus surface and the surface of plexus in the individual ventricles increases. The size of plexus in each ventricle expressed as a % of the total surface area of choroid plexus changes greatly in the early stages. In the smallest brains, the choroid plexus of the 4th ventricle amounts to 95%, while the 3rd ventricle plexus is still undeveloped. In the largest brains the plexus in the fourth ventricle amounts to 45% and in the 2 lateral ventricles together, 48% of the total plexus surface. The choroid plexus constitutes on average 27% of the total wall area of the ventricular system in the largest brains. In the 4th ventricle the plexus constitutes 50% and in the lateral ventricles 24% of the wall area. The results are compared with earlier studies, carried out on human brain ventricles, where the choroid plexus constitutes 63% of the total ventricular surface. The relative size of the individual ventricles expressed by their surface area (ependyma + choroid plexus) in % of the total surface of the ventricular system has been calculated. The lateral ventricles make an increasing contribution with increasing brain volume and in the largest brains these ventricles together constitute 53%. In 9 of 14 embryo brains, with a volume over 20 cu mm, coarctatio ventriculi was present. The area of this was measured to investigate how large an area of ependyma is involved.