DEMONSTRATION OF POLY-N-ACETYL LACTOSAMINE RESIDUES IN AMEBOID AND RAMIFIED MICROGLIAL CELLS IN RAT-BRAIN BY TOMATO LECTIN-BINDING

This study was designed to demonstrate the localization of poly-N-acet yl lactosamine residues in postnatal and adult rat brain, visualized b y their specific binding to a lectin obtained from Lycopersicon escule ntum (tomato). Lectin histochemistry was carried out on cryostat, para ffin, and vibratome sections and was examined by light microscopy. Sel ected vibratome sections were professed for electron microscopy. Our r esults showed that tomato lectin histochemistry was found in relation to blood vessels and glial cells in both postnatal and adult rat brain . Since tomato lectin-positive glial cells did not show GFAP immunorea ctivity and displayed the same morphological features and overall dist ribution as nucleoside diphosphatase (NDPase)-positive cells, they wer e consequently identified as microglial cells. At the electron microsc opic level, both ameboid and ramified microglial cells displayed intra cytoplasmic and plasma membrane lectin reactivity. In postnatal brain, ameboid microglial cells always showed stronger binding of tomato lec tin compared with ramified microglial cells in the adult brain. The pu tative significance of this decrease in poly-N-acetyl lactosamine from ameboid to ramified microglial cells and the possible role(s) of this sugar residue are discussed.