An ultrastructural study of the phagocytic activity of astrocytes in adult rat brain.

The role of adult astrocytes in the removal of cell debris and foreign particles following injury to the brain is controversial. This study was undertaken to elucidate the response of adult astrocytes to needle injury of the rat cerebral cortex, using a suspension of colloidal carbon as a marker for phagocytosis. Either a single or 2 successive injections of colloidal carbon suspension were made into the cerebral cortex. The animals were allowed to survive for periods of from 1 to 30 d. Unequivocal involvement of astrocytes in the removal of carbon particles was evident only in those brains which had been subjected to 2 successive injections of carbon. The particles were located in membrane-bound vacuoles and were subsequently sequestered in lysosomes. Carbon-containing astrocytes were observed in the immediate vicinity of the lesion, in the adjacent parenchyma, around blood vessels and abutting carbon-containing macrophages. This study demonstrates that adult astrocytes are involved in phagocytosis, but only as a second line of defence. The possible significance of carbon-laden astrocytes further away from the site of the lesion is discussed.