The comparison of microglia maturation in different structures of the human nervous system.

The aim of the study was to find out whether differences in morphology and time-sequence of microglia appearance in course of development of the phylogenetically different structures of the central nervous system (CNS) in normal human fetus do exist. An attempt was also made to evaluate quantitatively the development of microglial cells in comparison to astroglia, taking into account their role in the structural and immunological maturation of the CNS. The study was performed on CNS tissue of frontal lobes, mesencephalon and cerebellum from 72 fetuses between 8 and 22 week of gestation (GW). Histochemical and immunohistochemical reactions were used as basic study methods. A quantitative evaluation of developing microglia and astroglia in all investigated structures was performed by counting the mean number of cells per 1 mm2. Morphological and ultrastructural patterns of the three basic types of microglia; ameboid, ramified active and ramified resting, were characterized. It was indicated that they emerge at the same time in all structures under study, except the ameboid microglia arising earlier in the mesencephalon. A quantitative evaluation revealed that the number of ameboid microglial cells decreased slightly in an early stage of fetal development. The number of ramified microglial cells between 11 and 22 GW increased in all structures. The highest values of ramified microglia were found in mesencephalon, and the lowest in white matter of cerebellum. The number of astroglial cells exceeded the increase in ramified microglia by several times in all structures.