A-B. In SR of CA3, DOR-SIG particles are found in the cytoplasm (A) and near the plasma membrane (B). C. A spine with a DOR-SIG particle on the plasma membrane is contacted by mossy-fiber terminals. sp, spine; T, terminal. mf-T, mossy fiber terminal. Triangle, on plasma membrane SIG; Chevron, near plasma membrane SIG; Arrow, cytoplasmic SIG. Scale bar = 500 nm.