Heterogeneity in synaptic transmission along a Drosophila larval motor axon

Nat Neurosci. 2005 Sep;8(9):1188-96. doi: 10.1038/nn1526. Epub 2005 Aug 14.


At the Drosophila melanogaster larval neuromuscular junction (NMJ), a motor neuron releases glutamate from 30-100 boutons onto the muscle it innervates. How transmission strength is distributed among the boutons of the NMJ is unknown. To address this, we created synapcam, a version of the Ca2+ reporter Cameleon. Synapcam localizes to the postsynaptic terminal and selectively reports Ca2+ influx through glutamate receptors (GluRs) with single-impulse and single-bouton resolution. GluR-based Ca2+ signals were uniform within a given connection (that is, a given bouton/postsynaptic terminal pair) but differed considerably among connections of an NMJ. A steep gradient of transmission strength was observed along axonal branches, from weak proximal connections to strong distal ones. Presynaptic imaging showed a matching axonal gradient, with higher Ca2+ influx and exocytosis at distal boutons. The results suggest that transmission strength is mainly determined presynaptically at the level of individual boutons, possibly by one or more factors existing in a gradient.

Publication types

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

MeSH terms

  • Animals
  • Animals, Genetically Modified
  • Axons / physiology*
  • Calcium Signaling / physiology
  • Calcium Signaling / radiation effects
  • Diagnostic Imaging / methods
  • Drosophila
  • Drosophila Proteins / deficiency
  • Drosophila Proteins / genetics
  • Electric Stimulation / methods
  • Evoked Potentials / physiology
  • Evoked Potentials / radiation effects
  • Gene Expression Regulation, Developmental / physiology
  • Immunohistochemistry / methods
  • Larva / physiology*
  • Luminescent Proteins / metabolism
  • Membrane Potentials / physiology
  • Motor Neurons / cytology*
  • Mutagenesis, Insertional / physiology
  • Neuromuscular Junction / cytology*
  • Neuromuscular Junction / physiology
  • Neuromuscular Junction / radiation effects
  • Patch-Clamp Techniques / methods
  • Synaptic Transmission / physiology*
  • Synaptic Transmission / radiation effects


  • Drosophila Proteins
  • Luminescent Proteins