Firstly, the intracellular localization of Arc was studied by immunocytochemistry (Fig. 2C and D). In estrogen-treated cells, Arc protein was strongly expressed in cytoplasm and also present in neuritic processes (arrow head, Fig. 2D), while the untreated group showed no expression of Arc protein (Fig. 2C). The perinuclear accumulations of Arc probably represent the vesicle transporting mechanisms which appear to concentrate Arc in juxtanuclear Golgi.