Mechanical tension contributes to clustering of neurotransmitter vesicles at presynaptic terminals. 

Scott Siechen, Shengyuan Yang, Akira Chiba and Taher Saif

Proceedings of the National Academy of Sciences,   August 4, 2009   vol. 106   no. 31   12611–12616 

http://www.pnas.org/gca?gca=pnas%3B106%2F31%2F12611&allch= 

Memory and learning in animals are mediated byneurotransmitters that are released from vesicles clustered at the synapse. Asa synapse is used more frequently, its neurotransmission efficiency increases,partly because of increased vesicle clustering in the presynaptic neuron.Vesicle clustering has been believed to result primarily from biochemicalsignaling processes that require the connectivity of the presynaptic terminal with the cell body, the centralnervous system, and the postsynaptic cell. Our in vivo experimentson the embryonic Drosophila nervoussystem show that vesicle clustering at the neuromuscular presynaptic terminaldepends on mechanical tension within the axons. Vesicle clustering vanishesupon severing the axon from the cell body, but is restored when mechanicaltension is applied to the severed end of the axon.Clustering increases when intact axons are stretched mechanically by pullingthe postsynaptic muscle. Using micro mechanical force sensors, we find that embryonic axons that have formed neuromuscularjunctions maintain a rest tension of about one nanonewton. If the resttension is perturbed mechanically, axons restore the rest tension either byrelaxing or by contracting over a period of about 15 min. Our results suggestthat neuromuscular synapses employ mechanical tension as a signal to modulatevesicle accumulation and synaptic plasticity.