Heterogeneity in synaptic transmission along a Drosophila larval motor axon.
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.
Guerrero
Giovanna
G
Department of Molecular and Cell Biology, 279 Life Sciences Addition, University of California Berkeley, Berkeley, California 94720, USA.
Reiff
Dierk F
DF
Rieff
Dierk F
DF
Agarwal
Gautam
G
Ball
Robin W
RW
Borst
Alexander
A
Goodman
Corey S
CS
Isacoff
Ehud Y
EY
D000818:Animals; D030801:Animals, Genetically Modified; D001369:Axons / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology / Q000528:radiation effects; D003952:Diagnostic Imaging / Q000379:methods; D004330:Drosophila; D029721:Drosophila Proteins / Q000172:deficiency / Q000235:genetics; D004558:Electric Stimulation / Q000379:methods; D005071:Evoked Potentials / Q000502:physiology / Q000528:radiation effects; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D007150:Immunohistochemistry / Q000379:methods; D007814:Larva / Q000502:physiology*; D008164:Luminescent Proteins / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D009046:Motor Neurons / Q000166:cytology*; D016254:Mutagenesis, Insertional / Q000502:physiology; D009469:Neuromuscular Junction / Q000166:cytology* / Q000502:physiology / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D009435:Synaptic Transmission / Q000502:physiology* / Q000528:radiation effects
D029721:Drosophila Proteins; D008164:Luminescent Proteins