Abstract
The ‘local vesicle population’ (LVP), namely the population of synaptic vesicles lying in a zone 0.25 μm wide adjacent to the presynaptic membrane, has been measured at synapses of rat superior cervical ganglia fixed for electron microscopy following experiments performed during a 60 min periodin vitro. The mean LVP of 78 synapses in three unstimulated control ganglia was 122.0 ± s.e. 5·9 vesicles μm-2. Ganglia fixed 1 min after 3 min 10 Hz tetani of the preganglionic nerve had a significantly (P<0.001) higher mean LVP (158.0 ± s.e. 5·0). Replacement of the Ca2+ of the bathing medium by Mg2+ for the final 30 min did not affect the mean LVP of unstimulated ganglia but prevented the increase following preganglionic stimulation. When a bathing medium with Mg2+ replaced by Ca2+, or when a drug such as caffeine, morphine or adrenaline was present for the final 30 min of the experimental period, preganglionic nerve stimulation reduced the mean LVP below the mean value in paired unstimulated ganglia.
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