Abstract
SummaryBackground Spontaneous "miniature" transmitter release takes place at low rates at all synapses. Long thought of as an unavoidable leak, spontaneous release has recently been suggested to be mediated by distinct pre- and postsynaptic molecular machineries and to have a specialized role in setting up and adjusting neuronal circuits. It remains unclear how spontaneous and evoked transmission are related at individual synapses, how they are distributed spatially when an axon makes multiple contacts with a target, and whether they are commonly regulated. Results Electrophysiological recordings in the Drosophila larval neuromuscular junction, in the presence of the use-dependent glutamate receptor (GluR) blocker philanthotoxin, indicated that spontaneous and evoked transmission employ distinct sets of GluRs. In vivo imaging of transmission using synaptically targeted GCaMP3 to detect Ca 2+ influx through the GluRs revealed little spatial overlap between synapses participating in spontaneous and evoked transmission. Spontaneous and evoked transmission were oppositely correlated with presynaptic levels of the protein Brp: synapses with high Brp favored evoked transmission, whereas synapses with low Brp were more active spontaneously. High-frequency stimulation did not increase the overlap between evoked and spontaneous transmission, and instead decreased the rate of spontaneous release from synapses that were highly active in evoked transmission. Conclusions Although individual synapses can participate in both evoked and spontaneous transmission, highly active synapses show a preference for one mode of transmission. The presynaptic protein Brp promotes evoked transmission and suppresses spontaneous release. These findings suggest the existence of presynaptic mechanisms that promote synaptic specialization to either evoked or spontaneous transmission.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 484-493 |
| Number of pages | 10 |
| Journal | Current Biology |
| Volume | 24 |
| Issue number | 5 |
| DOIs | |
| State | Published - Mar 3 2014 |
| Externally published | Yes |
Bibliographical note
Funding Information:We thank members of the Isacoff lab for helpful discussions and support, Grant Kauwe and Tracey Kim for generating the SynapGCaMP3 fly line, and Robert S. Zucker for comments on an earlier version of this manuscript. We also thank Aaron DiAntonio and Stephan Sigrist for gifts of fly strains and antibodies and Loren Looger for the gift of the GCaMP3 construct. This work was supported by the National Science Foundation (FIBR 0623527) and a National Science Foundation Graduate Research Fellowship (DGE 1106400, Z.L.N.).