Abstract
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.
*Note: In the version of this article initially published online, the second author’s name was misspelled. The correct spelling should be Dierk F Reiff. The error has been corrected in the HTML version of the article. This correction has been appended to the PDF and print versions.
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04 September 2005
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Acknowledgements
We thank D. Raymond for developing the Bouton Project software; K. Zito for initial cloning and transfection of synapcam3.1 and M.-M. Poo, R. Zucker and M. Neff for comments on the manuscript. This work was funded by a US National Institutes of Health grant (E.Y.I. and C.S.G.), the Max-Planck-Society (D.F.R. and A.B.) and the Howard Hughes Medical Institute (G.G. and C.S.G.).
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Supplementary information
Supplementary Fig. 1
The relative increase in ΔFRET or decrease in current after two stimuli is smaller for postsynaptic terminals and NMJs with higher transmission. (PDF 267 kb)
Supplementary Fig. 2
GluR identity and distribution cannot explain the proximal-distal gradient of transmission strength. (PDF 4397 kb)
Supplementary Fig. 3
Differences between boutons in the number of active zone patches or the total quantity of an active zone marker cannot explain the proximal-distal gradient of transmission strength. (PDF 340 kb)
Supplementary Fig. 4
Possible origins for a presynaptic gradient of transmission strength. (PDF 553 kb)
Supplementary Table 1
Recording conditions and synapcam3.1 expression do not affect the physiological properties of the NMJ. (PDF 77 kb)
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Guerrero, G., Reiff, D., Agarwal, G. et al. Heterogeneity in synaptic transmission along a Drosophila larval motor axon. Nat Neurosci 8, 1188–1196 (2005). https://doi.org/10.1038/nn1526
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DOI: https://doi.org/10.1038/nn1526
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