A morphometric evaluation of morphological types of microglia and astroglia in human fetal mesencephalon.

Quantitative changes associated with the differentiation of microglial and astroglial cells in 48 fetal mesencephalons between 8 and 22 week of gestation (GW) were studies. Using lectin (RCA-1) labelling, two morphological types of RCA-1 positive cells, ameboid microglia (AM) and ramified microglia (RM) were identified on the basis of the cell body shape and the configuration of cytoplasmic processes. Astrocytes (AS) were identified by immunocytochemical labelling of GFAP. Measurements of microglial and astroglial cells were carried out in mesencephalon tectum and tegmentum under the microscope in sequential segments corresponding to equal sized non-overlapping areas. The quantitative data about concerning the number and percentage distribution of AM, RM and AS from each of the grid-quartiles were analyzed. The study revealed a time-sequence of appearance, characteristic pattern of distribution along perpendicular and longitudinal axes originating from aqueduct and changes in percent distribution of both types of microglial cells and astrocytes. Ameboid type of microglia was already present in 8 GW fetus in tectum (22.5 cells/mm2) and in tegmentum (10.2 cells/mm2). During the fetal development the number of AM peaked about 8-9 GW in tectum, accounting for 29 cells/mm2 close to aqueduct, and about 11-12 weeks in tegmentum, reaching 10.2-11 cells/mm2 close to aqueduct. As the fetus development advanced, the number of AM cells both in tectum and tegmentum was slowly dropped down reaching about 1.0 cells/mm2 in 20-22 GW. The ramified microglial cells as well as astroglial cells emerged in the fetal mesencephalon after 11 GW. A quantitative study also revealed a rapid increase in the density of RM in 13-16 GW (6.3 cells/mm2-close to aqueduct) and AS cells in 13-16 GW (36 cells/mm2-close to aqueduct) and later a decrease in cell number was observed. Similarly to AM, changes in the number of RM and AS cells were stabilized to about 20-22 GW. The percentage distribution of each type of microglia and astrocyte cells both in tectum and tegmentum differed markedly during the fetus development depending on the localization along the axes.