Spatio-temporal pattern of proliferation of immunoglobulin G-containing astrocytes in the injured mouse cerebral hemisphere.

Following a mechanical injury of the cerebral hemisphere in adult mice, [3H]thymidine was injected at different time intervals to reveal proliferating cells. Brain sections were double immunostained for immunoglobulin G (IgG) and glial fibrillary acidic protein (GFAP), and subjected to autoradiography. The procedure allowed to distinguish four cell types: (1) proliferating process-bearing cells immunopositive for IgG but expressing no GFAP (GFAP-/IgG+ PB cells) (2) proliferating and (3) non-proliferating astrocytes immunopositive both for GFAP and IgG (GFAP+/IgG+), (4) proliferating astrocytes expressing GFAP and containing no IgG (GFAP+/IgG-). Thereafter, the distribution of each cell type within the injury area was recorded at each stage of the experiment and displayed as contour line maps. During the whole posttraumatic period, areas of very strong proliferation of GFAP-/IgG+ PB-cells were located within deep layers of the cerebral cortex and in the white matter around the bottom part of the lesion. Few proliferating GFAP+/IgG+ astrocytes were mainly located in the same regions. However, changes in the distribution of proliferating astrocytes containing no IgG followed different spatio-temporal pattern. On the 4th day after injury areas of their proliferative activity surrounded both the bottom and superficial parts of the lesion. It seems that the immediate contact with the extravasated blood serum does not determine IgG cellular uptake. The uptake appears to depend on the cell type and its role in re-establishing the extracellular space in the injured brain tissue.