Surface fine structure of supraependymal elements and ependyma of hypothalamic third ventricle of mouse

The ependymal surface of the hypothalamic third ventricle of the adult female and male mouse was examined with the scanning electron microscope. The material was dried with the critical point method. Supraependymal cells, exhibiting a variety of forms, lie among the cilia of the rostrodorsal two-thirds of the ventricle. The cell bodies are usually between 8 and 10 mu in diameter and have dividing pseudopodial processes which may be broad or narrow, flat or stout, smooth or varicosed. The textured surfaces of the cells seen in this material appear to have no cilia, microvilli or membraneous folds though they may have small bleb-like protrusions. Some cells and adjacent cilia bear clusters of friable-looking material that may be secretory. In several female mice, mounds of debris, that could be degenerating cells or secretory material, were seen in intimate association with clusters of cells. The cells' processes extend over and through the surface of the mound. While some supraependymal cells may be neurons or glia, it is suggested that many of the cells seen may be morphological variants of one cell line, mononuclear phagocytes. Sausage-shaped structures at the end of long cilia-like stalks are described and their possible identity discussed.