Morphologic alterations of synapses in electrically stimulated superior cervical ganglia of the cat.

Prolonged preganglionic stimulation produces marked ultrastructural changes in presynaptic endings, which develop larger zones of contact with post-synaptic dendrites. Profiles of such endings, compared to controls, have fewer synaptic vesicles, similar areas, and greater circumferences. These results are compatible with the hypothesis that synaptic vesicles become incorporated into the plasma membrane during stimulation.