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 network of elongate components directly linked to synaptic vesicles and the presynaptic membrane. Each vesicle at the active zone that lies adjacent to the presynaptic plasma membrane has several such connections. Information provided by reconstruction data may be useful in generating experiments aimed at understanding the mechanisms involved in the docking of synaptic vesicles and their exocytosis during synaptic transmission. Nous avons utilisé la tomographie ME pour examiner aux électrons la structure fine du matériel dense apparemment amorphe qui est observé au niveau des zones actives des terminaisons axonales en microscopie électronique conventionnelle 2D. Des reconstructions 3D obtenues à partir de coupes sériées de 1 nm font apparaître un matériel constitué d'un réseau connectif de composés directement liés aux vésicules synaptiques et à la membrane présynaptique.