Microglial cells of the rat brain in postnatal period (comparative immunocytochemical analysis)

In the course of the brain’s development, distribution of microglial cells was studied in rats using immunocytochemical detection. To identify the microglial cells, antibodies to lipocortin 1 (LC1) and phosphotyrosine (PT) were used. On postnatal day 1, LC1-positive microglial cells of an ameboid shape were distributed mainly in the subventricular zone; their mean density was 31±8 cells/mm² (counted across the total area of frontal sections). On postnatal day 7, microglial cells of an intermediate type were located throughout the whole brain; their density was 54±15 cells/mm². On the 15th day, LC1-positive cells were of a ramified shape, and their density reached 104±20 cells/mm² (the microglial cell density in the mature normal brain was 103±3 cells/mm²). On postnatal day 7, PT-positive cells were similar in their morphology to LC1-positive cells of an intermediate type, while their mean density was 32 cells/mm². In the mature brain, the density of PT-positive microglia was 53±5 cells/mm²; the shape of the cells in the white and gray matter of the brain was, on the whole, similar to that of LC1-positive microglia. Therefore, LC1 is a specific marker for different types of microglial cells in the developing brain. Our data about 3D distribution and morphological peculiarities of microglial cells at different stages of postnatal development are consistent with the hypothesis on the neuroectodermal origin of microglia.