Microglia and astrocytes in the adult rat brain: comparative immunocytochemical analysis demonstrates the efficacy of lipocortin 1 immunoreactivity

The distribution of glial cells (microglia and astrocytes) in different regions of normal adult rat brain was studied using immunohistochemical techniques and computer analysis. Lipocortin 1, phosphotyrosine, and lectin GSA B(4), were used for identification of microglia, while S100beta and glial fibrillary acidic protein identified astrocytes. Bioquant computerized image analysis was used to quantify and map the immunostained cells in sections from adult rat brain. If lipocortin 1 was used as a marker, more microglial cells were detected than with phosphotyrosine or lectin. The lipocortin 1-positive microglial population was most numerous (on average, 130+/-5 cells/mm(2) of the brain section area) in neostriatum, and least (51+/-4 cells/mm(2)) in cerebellum and medulla oblongata. In general, the density of lipocortin 1 microglia was higher in the forebrain, and lower in the midbrain, and the least in the brainstem and cerebellum. The number of S100beta astrocytes was two to three times larger than the number of microglial cells, and approximately two times greater than glial fibrillary acidic protein cells. A high density of astrocytes was found in the hypothalamus and hippocampus (more than 260 cells/mm(2)); they were more numerous in the white matter than in the gray matter. Fewer astrocytes were observed in the cerebral cortex, neostriatum, midbrain, medulla oblongata and cerebellum (less than 200 cells/mm(2)). Thus lipocortin 1 and S100beta were shown to be the most specific and reliable markers for microglia and astrocytes, respectively. The regional population differences demonstrated for lipocortin 1 microglia and S100beta astrocytes presumably reflect structural and functional specializations of the certain brain regions.