Lectin binding sites and anionic components related to differentiation in the prenatal rat cerebral cortex.

The location of lectin binding sites and of anionic components was studied in the embryonic rat cerebral cortex after the formation of the cortical plate at embryonic day 18. The cortical layers advanced in differentiation, i.e. the sub-plate region and the marginal zone, showed a predominant staining with peroxidase conjugates of wheat germ agglutinin (WGA), peanut agglutinin (PNA), and after immunocytochemical detection of PNA binding sites. This pattern was obtained also with the colloidal iron hydroxide staining method. In contrast to this, the binding of concanavalin A and of succinylated WGA did not reveal a prevalent staining of the sub-plate region and the marginal zone. The further histochemical analysis of the substances responsible for the selective staining of these layers was performed by lipid extractions and by enzymatic treatment of the tissue sections with trypsin, hyaluronidase or neuraminidase prior to the binding of lectins or colloidal iron. The results obtained indicated high concentrations of sialylated galactosylglycoproteins in coexistence with glycosaminoglycans. Electron microscopy was performed with peroxidase conjugates of WGA and PNA. Binding sites of both of the lectins in the sub-plate region and in the marginal zone were located mainly at cell surfaces of the different cellular structures. The most intensive binding of WGA and PNA was detected at the surface membranes and at intracellular material of amoeboid microglial cells and astrocyte-like cell processes. It can be concluded that in distinct brain areas during early differentiation specific glycoproteins in coexistence with glycosaminoglycans are situated at, or associated with cell surfaces in high concentrations. The identical histochemical features previously described in mesenchymal tissues suggest that these glycoconjugates might be related to common morphogenetic processes in which non-neuronal cells of brain and body are specifically involved.