[The development of epiplexus cells (Kolmer cells) in the choroid plexus of the fourth ventricle of the mouse. A scanning and transmission electron microscopic study].

The development of the epiplexus cells (Kolmer cells) on the surface of the choroid plexus of the mouse fourth ventricle was investigated with scanning and transmission electron microscopy between the 11th day post conceptionem and the 20th day post partum. On the 11th day of development rounded cells with a bulbous surface are scattered throughout the ventricular surface of the plexus "anlage". They are characterized by a strongly vacuolated cytoplasm containing long cisterns of granular endoplasmic reticulum. The nucleus is indented. In the further stages of development (day 14 to day 16) epiplexus cells of different shape overlay the plexus epithelium. They are provided with filopodium-like processes spreading over two or more plexus cells. They differ in the content of intracytoplasmic vacuoles and electron density. The study of the early postnatal stages of development shows that the outer aspect of the epiplexus cells do not change very much from birth to 20 days post partum. The ability of phagocytosis in developing epiplexus cells was studied by intraventricular injection of horseradish peroxidase on day 11, 16 and 18 post conceptionem. Great amounts of tracer molecules could be demonstrated in epiplexus cells of 16 and 18 day-old embryos.