title: Evoked and spontaneous transmission favored by distinct sets of synapses.
abstract: BACKGROUND
  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.
authors.affiliation: Department of Molecular and Cell Biology, 271 Life Sciences Addition, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Einat S
authors.initials: ES
authors.lastname: Peled
authors.affiliation: Department of Molecular and Cell Biology, 271 Life Sciences Addition, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Zachary L
authors.initials: ZL
authors.lastname: Newman
authors.affiliation: Department of Molecular and Cell Biology, 271 Life Sciences Addition, University of California, Berkeley, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, 450 Li Ka Shing Biomedical Center, University of California, Berkeley, Berkeley, CA 94720, USA; Physical Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. Electronic address: ehud@berkeley.edu.
authors.forename: Ehud Y
authors.initials: EY
authors.lastname: Isacoff
mesh_terms: D000818:Animals; D004330:Drosophila / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D005071:Evoked Potentials; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007814:Larva; D009469:Neuromuscular Junction / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology; D017470:Receptors, Glutamate / Q000378:metabolism; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D020692:rab3 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C510146:BRP protein, Drosophila; D029721:Drosophila Proteins; D018691:Excitatory Amino Acid Antagonists; D017470:Receptors, Glutamate; D020692:rab3 GTP-Binding Proteins