Optical quantal analysis of synaptic transmission in wild-type and rab3-mutant Drosophila motor axons

Nat Neurosci. 2011 Apr;14(4):519-26. doi: 10.1038/nn.2767. Epub 2011 Mar 6.


Synaptic transmission from a neuron to its target cells occurs via neurotransmitter release from dozens to thousands of presynaptic release sites whose strength and plasticity can vary considerably. We report an in vivo imaging method that monitors real-time synaptic transmission simultaneously at many release sites with quantal resolution. We applied this method to the model glutamatergic system of the Drosophila melanogaster larval neuromuscular junction. We find that, under basal conditions, about half of release sites have a very low release probability, but these are interspersed with sites with as much as a 50-fold higher probability. Paired-pulse stimulation depresses high-probability sites, facilitates low-probability sites, and recruits previously silent sites. Mutation of the small GTPase Rab3 substantially increases release probability but still leaves about half of the sites silent. Our findings suggest that basal synaptic strength and short-term plasticity are regulated at the level of release probability at individual sites.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Axons / metabolism
  • Axons / physiology*
  • Drosophila melanogaster
  • Motor Neurons / cytology
  • Motor Neurons / metabolism*
  • Mutation / genetics*
  • Neuromuscular Junction / cytology
  • Neuromuscular Junction / genetics*
  • Neuromuscular Junction / metabolism
  • Neuronal Plasticity / genetics
  • Presynaptic Terminals / metabolism*
  • Presynaptic Terminals / ultrastructure
  • Probability
  • Synaptic Transmission / genetics*
  • Synaptic Vesicles / genetics
  • Synaptic Vesicles / metabolism
  • Synaptic Vesicles / ultrastructure
  • Voltage-Sensitive Dye Imaging / methods*
  • rab3 GTP-Binding Proteins / genetics*


  • rab3 GTP-Binding Proteins