Different Modes of Synaptic Vesicle Recycling un Synaptophysin-pHluorin Transgenic Mouse Motor Nerve Terminals

Abstract

In the present work, a new tool for studying synaptic vesicle exo- and end ... The adult vertebrate NMJ is a highly reliable synapse that must exocytose a large number of vesicles with each stimulus to guarantee effective excitation of the postsynaptic muscle fiber. To maintain effective synaptic transmission, the motor nerve terminal must be able to reuse vesicles by subsequent endocytosis. Diverse modes of endocytosis seem to coexist in the same motor terminal although their relative contribution and regulation mechanisms are not completely clear yet. In the first part of this work, we used dynasore, a blocker of the GTPase activity of dynamin 1/2, to investigate the contribution of dynamin in endocytosis at the presynaptic terminal, during and following high frequency stimulation trains. If endocytosis during stimulation is dynamin 1/2-dependent, SypHy would remain in the plasma membrane and the fluorescence would be larger in the presence of the drug. On the other hand, if dynamin 1/2 is activated after the stimulus, slowness of the signal is expected. Our experiments suggest that dynamin 1/2 only modestly, and in a time-dependent manner, participates in endocytosis during repetitive stimulation. After stimulation, however, dynamin 1/2 is rapidly activated. In addition, we demonstrated by immunolabeling that dynamin 1 and dynamin 3 are co-expressed in the motor nerve terminals, suggesting that dynamin 1/2-independent mechanisms also exist in this synapse.|