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

Heterogeneity in synaptic transmission along a Drosophila larval motor axon.

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Department of Molecular and Cell Biology, 279 Life Sciences Addition, University of California Berkeley, Berkeley, California 94720, USA.

Erratum in

  • Nat Neurosci. 2005 Oct;8(10):1411. Rieff, Dierk F [corrected to Reiff, Dierk F].


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.

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