Lectin labelling of amoeboid and ramified microglial cells in the telencephalon of ovine fetuses with the B4 isolectin from Griffonia simplicifolia.

The topographical distribution of amoeboid and ramified microglial cells in the telencephalon of sheep fetuses at 60-149 days of gestation was examined by lectin histochemistry. Biotinylated B4 isolectin from Griffonia simplicifolia labelled both types of cell in coronal paraffin wax sections fixed in different fixatives. The most intense staining was seen in sections fixed in Bouin's fluid. Pretrypsinization of formaldehyde- and paraformaldehyde-fixed sections resulted in marked enhancement of staining affinity. In fetuses aged 60 to 96 days numerous amoeboid microglial cells were present in subependymal regions of the lateral ventricles, in the septum pellucidum, within the cavum septum pellucidum, in the corpus callosum, and in the internal and external capsule. From 84 days of gestational age onwards the occurrence of ramified microglial cells was noted. Thereafter, amoeboid microglia gradually disappeared and, in two fetuses examined at term, lectin-positive amoeboid microglial cells were no longer detectable in the telencephalic parenchyma. The distribution of amoeboid microglial cells was similar to that described in rodent brain, but the earlier disappearance of this cell type from the ovine telencephalon was interpreted as a reflection of the more rapidly proceeding brain development in the sheep than in other vertebrates.