Accumulation of delicate tubulovesicular elements in presynaptic axon terminals in aged SMG-CG. (A–C) Presynaptic nerve terminals show anastomosing tubulovesicular elements (arrows) in close apposition to the active zone and admixed with agranular synaptic vesicles. Magnification bars: A, 500 nm; B, 100 nm; C, 500 nm. (D, E) Intimate association of agranular and heterogeneous agranular elements with tubulovesicular elements. Magnification bars: D, E, 500 nm. (F) Tubulovesicles may form connections with the axolemma (arrow). Magnification bar: 500 nm. (G) Progressive enlargement of presynaptic nerve terminals is dominated by delicate tubulovesicular elements. Magnification bar: 500 nm. (H) Typical dystrophic axon (arrow) is large with compact tubulovesicular elements. Magnification bar: 2 μm.