A comparative study of the intracellular lectin binding sites of neurons in culture with neurons in situ

Abstract

The cytochemical properties of intracellular membrane systems which are likely to be subcellular sites of glycoprotein oligosaccharide synthesis and trafficking have been compared in cultured neuroblastoma cells (as a potential model system) and in Purkinje neurons of rat cerebellum. In aldehyde-fixed N18 cells, permeabilized with Triton X-100, concanavalin A (Con A) binding sites were found in the somata, neurites, and growth cones. Con A binding sites in growth cones appeared as a fine, membranous network. Wheat germ agglutinin (WGA) binding sites were restricted to the perinuclear region of the soma and to the distal tips of growing neurites. As shown previously, Purkinje cell somata and presynaptic terminals also contain Con A binding sites. In this study, WGA and succinylated WGA binding sites were observed in the presynaptic terminals of Purkinje cells. Neuraminidase enzyme digestion prior to lectin labeling removed or greatly reduced WGA binding in the neuropil of the deep nucleus but not in presynaptic terminals of Purkinje cells. Succinylated WGA binding sites were not affected by neuraminidase digestion. Neuraminidase digestion also exposed Ricinis communis agglutinin I binding sites in the neuropil and in synaptic terminals of Purkinje cells. These results in combination with previous studies of intracellular lectin cytochemistry of neurons in the central nervous system demonstrate the similarity of these cells to neuroblastoma cells in their intracellular lectin binding characteristics. Results of the lectin cytochemical studies after neuraminidase digestion of presynaptic terminals support the possibility that neurons may use a post- or extra-Golgi system for the addition of peripheral sugars to the oligosaccharides of certain glycoproteins destined for the cell surface.