Fig. 1. Criteria for recording of immunogold particles as associated with synaptic-like micro vesicles (SLMVs), or secretory granule (SG) limiting membranes (thick contours). Gold particles (and grid points for area determination) with centres within 30 nm of the limiting membranes of SLMVs or SGs were included (grey areas), omitting ones closer to SG dense cores than 15 nm. Particles within 30 nm of the surface of mitochondria (or other, rarer organelles) were excluded from recording (see text).