Association between Synaptic Vesicles and Neurotubules

Abstract

NUMEROUS electron microscopic studies of peripheral axons and central ganglia of vertebrates and invertebrates have supported two hitherto unrelated generalizations. These are, first, that the chief axoplasmic components, extending beyond the neurone cell body, are neurofilaments and neurotubules; second, that these structures are accompanied by concentrations of small axoplasmic vesicles where a chemically mediated synapse is established with the surface of an adjacent excitable cell. While it has often been suggested^1–3 that these “synaptic vesicles” contain transmitter molecules discharged into the intercellular gap between pre- and post-synaptic surfaces when excitation reaches the nerve junction, it is by no means clear how the vesicles are charged with transmitter, for, in contrast to the situation in neurosecretory cells where visible products pass into the axon from the cell body, synaptic vesicles have not been observed to follow this route.