Fig. 3. NCS-1 immunoreactivity is associated with the ER. Ultrathin frozen sections from rat brain cortex (A,C,D) and hippocampus (B) were immunostained for NCS-1 (A,B) or double immunolabeled (C,D) for NCS-1 (18 nm gold particles) and PDI (12 nm gold particles). NCS-1 immunoreactivity is visible in the cytoplasm and, to a lesser extent, on tubulovesicular structures (A-D, arrowheads). In these structures, NCS-1 (arrowheads) colocalizes with the ER marker PDI. No labeling is detectable on mitochondria (m), lysosmes (L) or nuclei (n). Bars, 200 nm.