Figure 394 from Chapter 15 (Cytoplasmic Inclusions) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. "Omega figures" capturing synaptic vesicle exocytosis at the synaptic junction. This event was observed during chemical stimulation of the frog neuromuscular junction, prepared by rapid freezing with liquid helium followed by freeze substition. 4-aminopyridine was used to trigger release of the neurotransmitter acetylcholine.Image by John Heuser and Tom Reese. A PDF copy of the accompanying chapter is available on the ASCB's BioEDUCATE website.