RCA-I LECTIN HISTOCHEMISTRY AFTER TRYPSINIZATION ENABLES THE IDENTIFICATION OF MICROGLIAL CELLS IN THIN PARAFFIN SECTIONS OF THE MOUSE-BRAIN

A biotinylated lectin from Ricinus communis (RCA-I) and avidin-biotin- horseradish peroxidase complex (ABC) were used to identify microglial cells in 3-mu m-thick sections of formalin-fixed paraffin-embedded bra ins of adult mice required for quantitative cell kinetic studies. In 3 -mu m-thick sections of the mouse brain the staining intensity of RCA- I-positive cells compared to background staining was too low for evalu ation, quite in contrast to rat brain. However, perikarya and cytoplas mic processes of microglial cells were clearly stained in 10- and 20-m u m-thick sections. The low contrast characteristic of thin mouse brai n sections could be enhanced by pre-incubating the sections with tryps in before application of the lectin. We assume that different densitie s of RCA-I binding sites among microglial cells of rats and mice, resp ectively, are responsible for the different staining intensities obser ved. Our protocol of lectin staining did not influence subsequent auto radiography for studies of cell proliferation after [H-3]thymidine app lication.