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

Nature Neuroscience volume 14, pages 519–526 (2011)Cite this article

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Abstract

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.

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Figure 1: Postsynaptically targeted GCaMP2 (SynapGCaMP2) reports single-action-potential, single-release-site Ca2+ influx.
Figure 2: SynapGCaMP2 imaging of sucrose-induced spontaneous release events.
Figure 3: Stimulation-evoked responses have same ΔF/F range of values as spontaneous events.
Figure 4: Comparison of release probabilities to locations of active zones in the NMJ.
Figure 5: The distal bouton is more active than other boutons along the axonal branch.
Figure 6: The distal bouton has more spontaneous (sucrose-induced) ΔF spots than other boutons along the axonal branch.
Figure 7: Paired-pulse stimulation facilitates low-probability sites and depresses high-probability sites.
Figure 8: Transmission properties of rab3-mutant NMJs.

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Acknowledgements

We thank R.S. Zucker for helpful discussions, G. Kauwe and G. Agarwal for help generating the SynapGCaMP2 fly line, H.L. Aaron for advice on imaging and J.A. Min for help with testing fly strains. We also thank A. DiAntonio for gifts of fly strains and for the Rab3 antibody. This work was supported by US National Science Foundation grant FIBR 0623527.

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Authors and Affiliations

  1. Department of Molecular and Cell Biology, University of California, Berkeley, California, USA

    Einat S Peled & Ehud Y Isacoff

  2. Helen Wills Neuroscience Institute, University of California, Berkeley, California, USA

    Ehud Y Isacoff

  3. Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA

    Ehud Y Isacoff

Authors
  1. Einat S Peled
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  2. Ehud Y Isacoff
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Contributions

E.S.P. carried out experiments and data analysis. E.Y.I. supervised the project. E.S.P. and E.Y.I. wrote the manuscript.

Corresponding author

Correspondence to Ehud Y Isacoff.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–9, Supplementary Table 1 and Supplementary Text (PDF 638 kb)

Supplementary Movie 1

Single action-potential evoked responses in the NMJ of Fig. 1. (MOV 71 kb)

Supplementary Movie 2

Spontaneous activity in the NMJ of Fig. 2. (MOV 547 kb)

Supplementary Movie 3

Responses to paired-pulse stimulation (NMJ of Fig. 7). (MOV 155 kb)

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Peled, E., Isacoff, E. Optical quantal analysis of synaptic transmission in wild-type and rab3-mutant Drosophila motor axons. Nat Neurosci 14, 519–526 (2011). https://doi.org/10.1038/nn.2767

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