Activation of phagocytotic activity of glial cells in corpus callosum in tissue cultures

Abstract

Summary Explants of the corpus callosum (c. c.) prepared from 12-day-old rats were cultivated in Rose chambers for 1 to 67 days. After 1, 7 and 8 days of cultivation indian ink (i. i.) suspension was added to the cultivation medium for 4 to 60 h . Phagocytosing cells were found already 4 h after administration of i. i. They appeared more frequently however only 2 to 3 days after application. Initially the incidence of phagocytes was relatively higher at the periphery of the fragment, especially where calls migrating later to the outgrowth zone were located. During the subsequent cultivation the relative number of phagocytes in the outgrowth zone increased. Toward the 10th day of cultivation 1/3 to 1/5 of the cell population of this zone contained i. i. particles. Cells with ingested i. i. particles were found even 67 days after being phagocytosed. When i. i. administered to 7- or 8-day-old cultures phagocytes were relatively more frequent in the explants with delayed migratory activity. A significantly lower number of phagocytosing cells was observed in explants prepared from older donor (30-day-old rats). Phagocytosed i. i. particles were found in mesenchymal and microglial-like cells as well as in the immature calls of microglial type; in the differentiated microglial cells phagocytosis was observed only rarely. The 3 H-thymidine-light-microscope autoradiograpby revealed that phagocytosing cells synthesized DNA only exceptionally and vice versa i. e. cells close to the S-phase phagocytosed i. i. very rarely. Electron microscopic observations (performed on cultures without the i. i. in the medium) showed numerous vacuoles and increased number of lysosomes in microglial- and mesenchymal-like macrophages and immature microglial cells. The vacuoles contained osmiophilic material and remnants of membranes. The lipoidic characater of the vacuoles is indicated also by Sudan staining. They were present both in the cell body cytoplasm and cell processes. In older cultures a part of these vacuoles could however originate from the intracellular autodigesting processes. Present results revealed o a) a high capacity of cells of the cultivated corpus callosum to phagocytosis which represent a part of the “cleaning reaction” in the tissue cultures and b) decrease in activation of explanted white matter to phagocytosis with the age of donors.