DISSECTION OF ACTIVE ZONES AT THE NEUROMUSCULAR-JUNCTION BY EM TOMOGRAPHY

We used EM tomography to examine the fine structure of the apparently amorphous electron dense material that is seen at active zones of axon terminals when viewed by conventional 2D electron microscopy. Serial 1-nm optical slices from 3D reconstructions of individual thin tissue sections reveal that the material is composed of an interconnecting ne twork of elongate components directly linked to synaptic vesicles and the presynaptic membrane. Each vesicle at the active zone that lies ad jacent to the presynaptic plasma membrane has several such connections . Information provided by reconstruction data may be useful in generat ing experiments aimed at understanding the mechanisms involved in the docking of synaptic vesicles and their exocytosis during synaptic tran smission. ((C) Elsevier, Paris).