In vivo uptake of wheat germ agglutinin-horseradish peroxidase conjugates into neuronal GERL and lysosomes.

In published studies we have shown that lectins and cholera toxin bind at 4 degrees C on surfaces in cultured neurons and neuroblastoma cells and, after incubations of labeled cells at 37 degrees C, undergo endocytosis (adsorptive endocytosis) into GERL (Golgi-endoplasmic reticulum-lysosome). In this study conjugates of wheat germ agglutinin (WGA) with horseradish peroxidase (HRP), or free HRP, were injected in rat submandibular glands or over superior cervical ganglia, and their uptake was examined by electron microscopic cytochemistry for HRP. Lysosomes and vesicles and cisternae of GERL were involved in the uptake of WGA-HRP injected into the submandibular gland or into the superior cerival ganglion; HRP, administered in a similar fashion, but in amounts 10-15-fold higher than WGA-HRP, underwent endocytosis into lysosomes. The present in vivo studies, as well as previous in vitro studies, indicate that neuronal GERL is part of the endocytic pathway of various ligands which bind on corresponding surface (plasma membrane) "receptors".