Cell proliferation in injured spinal cord. An electron microscopic study.

Abstract

AbstractTo examine the fine structure of cells synthesizing DNA in the spinal cord in response to injury, mice were given a single injection of 3H‐thymidine two days after stab injury to the spinal cord and were sacrificed at either two hours or one, two, six or 14 days later. The most common type of labeled cell found at a distance from the wound at all the time intervals after 3H‐thymidine injection had an elongated or irregularly oval nucleus with clumps of condensed chromatin at the nuclear envelope and one or more nucleoli. The cytoplasm which was darker than adjacent axoplasm, contained dense bodies, scattered mitochondria, many free ribosomes, only a few rather long cisternae of granular endoplasmic reticulum, a prominent Golgi apparatus, and a few granules. These cells were similar in appearance to the cells that have been identified as microglia or multipotential glia by others. However, they also have many features in common with blood mononuclear cells. In the wound, in addition to the cells already described, the labeled cells at two hours after 3H‐thymidine injection included well developed macrophages, a few endothelial cells, and a large number of cells with large pale nuclei and cytoplasm containing abundant microtubules and granules. At the later time intervals, these cells apparently developed large numbers of cytoplasmic filaments. Although they bore some resemblance to reactive astrocytes, these labeled cells were not typical astrocytes, and their location, their apparent transformation from a cell without filaments, and their pseudopodia and surface vacuoles suggest the possibility that they may be derived from blood mononuclear cells.