Effects of trypsinization and microwave treatment on lectin labelling of microglial cells in paraffin-embedded sections from pre- and postnatal bovine brains.

The effects of microwave heat treatment on lectin histochemical staining of microglial cells with Griffonia simplicifolia B4 isolectin (GSA I-B4) and Ricinus communis agglutinin-I (RCA-I) in paraffin-embedded pre- and postnatal bovine brain tissue fixed in two different fixatives (Bouin's fluid and 4% neutral buffered formaldehyde) were examined, and the results compared with lectin labelling obtained in untreated and trypsinized serial sections. The results indicate that lectin labelling of bovine microglial cells depends on the kind of lectin applied, the fixative used for tissue preservation, the isotype of microglia to be labelled, and the pretreatment of tissue sections. In brain tissue fixed in Bouin's fluid, GSA I-B4 staining of both microglial isotypes, i.e., amoeboid and ramified microglial cells, was achieved without trypsinization. Staining of sections with RCA-I, however, yielded negative results both on untreated and on trypsinized sections. These findings suggest that species-specific differences in the density of binding sites accessible to GSA I-B4 and RCA-I, respectively, may exist. Pretreatment of sections by microwave irradiation had different effects depending on the lectin and fixative used and on the microglial isotype to be stained. Microwave heat treatment of sections prior to incubation with RCA-I enabled the labelling of amoeboid and ramified microglial cells. The latter cell type, however, was exclusively stained in brain tissue fixed in Bouin's fluid. With GSA I-B4, exclusively the labelling of ramified microglial cells in sections fixed in Bouin's fluid was improved. It is assumed that by microwave pretreatment of sections from bovine brain the access of both lectins to their receptors, i.e., D-galactose residues on microglial cells, may be facilitated.