On synaptic vesicles, complex vesicles and dense projections

Abstract

Observations support the view that in vertebrates synaptic vesicles are produced by liberation from complex vesicles, which in turn are derived from the membranes of the presynaptic bag. Some of the shell fragments of the complex vesicles remain in the bag, whereas other fragments of the shell adhere to the wall of the synaptic vesicle. It is suggested that the dense projections on the presynaptic membrane may be partly or wholly composed of these fragments, i.e., the ones that project from the surfaces of the synaptic vesicles that lie clustered against the presynaptic membrane. Of the various fixation techniques used, some show vesicle membranes clearly but not the shells; others show the shells best; others show both the shells and the vesicles.