Spontaneous neurotransmission at evocable synapses predicts their responsiveness to action potentials
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Synaptic transmission relies on presynaptic neurotransmitter (NT) release from synaptic vesicles (SVs) and on NT detection by postsynaptic receptors. Transmission exists in two principal modes: action-potential (AP) evoked and AP-independent, “spontaneous” transmission. AP-evoked neurotransmission is considered the primary mode of inter-neuronal communication, whereas spontaneous transmission is required for neuronal development, homeostasis, and plasticity. While some synapses appear dedicated to spontaneous transmission only, all AP-responsive synapses also engage spontaneously, but whether this encodes functional information regarding their excitability is unknown. Here we report on functional interdependence of both transmission modes at individual synaptic contacts of Drosophila larval neuromuscular junctions (NMJs) which were identified by the presynaptic scaffolding protein Bruchpilot (BRP) and whose activities were quantified using the genetically encoded Ca2+ indicator GCaMP. Consistent with the role of BRP in organizing the AP-dependent release machinery (voltage-dependent Ca2+ channels and SV fusion machinery), most active BRP-positive synapses (>85%) responded to APs. At these synapses, the level of spontaneous activity was a predictor for their responsiveness to AP-stimulation. AP-stimulation resulted in cross-depletion of spontaneous activity and both transmission modes were affected by the non-specific Ca2+ channel blocker cadmium and engaged overlapping postsynaptic receptors. Thus, by using overlapping machinery, spontaneous transmission is a continuous, stimulus independent predictor for the AP-responsiveness of individual synapses.
Originalsprog | Engelsk |
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Artikelnummer | 1129417 |
Tidsskrift | Frontiers in Cellular Neuroscience |
Vol/bind | 17 |
ISSN | 1662-5102 |
DOI | |
Status | Udgivet - 2023 |
Bibliografisk note
Funding Information:
MJ was funded by a PhD-fellowship from the Einstein Center for Neurosciences Berlin. This work was funded by grants from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation): Project-ID 278001972, TRR 186 and Project-ID 261020751, Emmy-Noether Programme to AMW. This work was also supported by the Novo Nordisk Foundation: Grant number: NNF19OC0056047, Young Investigator Award to AMW.
Publisher Copyright:
Copyright © 2023 Grasskamp, Jusyte, McCarthy, Götz, Ditlevsen and Walter.
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