Fig. 2

Three types of SSC are classified in dissociated hippocampal neurons (top panels) and in hippocampal slice cultures (lower panels): Type A – a single stack of ER with an open cistern (open arrows in a & d). Type B – a single stack of ER with a segment of flattened cistern (large black arrows in b & e). There is barely any discernible lumen in the flattened segment, and the gap between the flattened segment and PM is filled with dark material (area between two short, small arrows in e). Type C – double stacks of ER with a flattened first stack (1) beneath the PM, and a second stack (2) below (1). The gap between the two stacks is filled with amorphous materials and the ER membranes facing the gap are typically devoid of ribosomes (white small arrows in f) that typically are attached on the ER membrane facing the cytoplasm. The distance between the two ER stacks are variable, ranging from 30 to 60 nm, in both culture systems. For example, the distance (double-headed arrow) is ~ 40 nm in (c), and ~ 60 nm in (f). In all three types of SSC, the gap between the first stack of ER and the PM is uniform at 10 nm (*), and the length of SSC is measured between the two long, small arrows on the PM in (a, b, d, e). Scale bar = 0.1 μm