Ultrastructure of supraependymal cells and ependyma of hypothalamic third ventricle of mouse

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Abstract
This study examines some ultrastructural features of the ependyma and supraependymal cells of hypothalamic third ventricle of the mouse in the region medial to the dorsomedial and ventromedial nuclei and dorsal part of infundibular nucleus. The brains of two males and 12 females in various phases of the estrous and reproductive cycle were studied.In the ependyma, large variations were found in the incidence of various organelles and surface features both among ependymal cells and among animals. These variations suggest that different ependymal cells have different functions and that the hypothalamic ependymal layer as a whole reflects in its morphology changing metabolic states of the animal.The main variations were found in the cytoplasm lying between the cell nucleus and ventricular surface. In some specimens the Golgi complexes were extensive and associated with many vesicles at the cell surface. Lipid‐like droplets may be large and abundant, sometimes bulging into the ventricle. Cytoplasmic surface protrusions may be large, irregular, and bulging with droplets, vacuoles or vesicles. These features, along with others, suggest a dynamic relationship between ependyma and cerebrospinal fluid (csf). Relations between tanycyte processes and neuropil are also described.Supraependymal cells varied in incidence, the largest numbers being found in a proestrous, an estrous and a lactating mouse. Their shape and nucleus, the abundance of dense bodies and lysosome‐producing structures and other features suggest that many supraependymal cells are macrophages. Noteworthy in some cells were bizarre imtochondrial profiles associated with Golgi, endoplasmic reticulum, lysosomes and lipid droplets (GERL and LERL)It is suggested that phagocytic supraependymal cells are engaged in processing the debris that results from changing metabolic activities, including secretion and exocytosis, blebbing and necrosis, of ependymal cells and also in the ingestion of foreign particles invading csf or ependyma.