The architecture of active zone material at the frog's neuromuscular junction

Active zone material at the nervous system's synapses is situated next to s ynaptic vesicles that are docked at the presynaptic plasma membrane, and ca lcium channels that are anchored in the membrane. Here we use electron micr oscope tomography to show the arrangement and associations of structural co mponents of this compact organelle at a model synapse, the frog's neuromusc ular junction. Our findings indicate that the active zone material helps to dock the vesicles and anchor the channels, and that its architecture provi des both a particular spatial relationship and a structural linkage between them. The structural linkage may include proteins that mediate the calcium -triggered exocytosis of neurotransmitter by the synaptic vesicles during s ynaptic transmission.