Demonstration of amoeboid and ramified microglial cells in pre- and postnatal bovine brains by lectin histochemistry.

In embryonic, fetal and postnatal bovine brains the development and distribution of microglial cells was examined by lectin histochemistry, using the isolectin B4 from Griffonia simplicifolia (GSA I-B4), the lectin from Ricinus communis (RCA-I), and mistletoe lectin (ML I). With GSA I-B4 and ML I, different types of microglial cells, i.e., amoeboid, intermediate and ramified cells, were specifically stained. On sections fixed in Bouin's fluid significantly higher numbers of microglial cells were labelled than on sections fixed in formalin. On the latter, proteolytic pretreatment was required. With RCA-I, no staining of microglial cells was achieved. This finding may indicate the presence of very low concentrations of beta-D-galactose residues on bovine microglial cells in comparison with other species studied so far. In the fetal telencephalon, the highest numbers of amoeboid microglial cells were found in transitory structures (subependymal regions of the lateral ventricles, cavum septi pellucidi, intermediate zone) and in areas of developing axon tracts (corpus callosum, internal and external capsules) between three and five months of gestational age. From 3-4 months of gestational age onward, the appearance of ramified microglial cells was noted. In 7-8 month-old fetuses, a complete change of the microglial cell picture occurred. Ramified cells clearly predominated, whereas amoeboid cells had markedly decreased. In 8-9 month-old fetuses, amoeboid microglial cells had almost disappeared from fetal brains. In brains from subadult and adult cattle, lectin-positive ramified microglial cells with up to five cellular processes were seen in all brain areas, located adjacent to vessels or surrounding neuronal perikarya.