Physical determinants of vesicle mobility and supply at a central synapse

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Abstract

Encoding continuous sensory variables requires sustained synaptic signalling. At several sensory synapses, rapid vesicle supply is achieved via highly mobile vesicles and specialized ribbon structures, but how this is achieved at central synapses without ribbons is unclear. Here we examine vesicle mobility at excitatory cerebellar mossy fibre synapses which sustain transmission over a broad frequency bandwidth. Fluorescent recovery after photobleaching in slices from VGLUT1^Venus knock-in mice reveal 75% of VGLUT1-containing vesicles have a high mobility, comparable to that at ribbon synapses. Experimentally constrained models establish hydrodynamic interactions and vesicle collisions are major determinants of vesicle mobility in crowded presynaptic terminals. Moreover, models incorporating 3D reconstructions of vesicle clouds near active zones (AZs) predict the measured releasable pool size and replenishment rate from the reserve pool. They also show that while vesicle reloading at AZs is not diffusion-limited at the onset of release, diffusion limits vesicle reloading during sustained high-frequency signalling.

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Jason Seth Rothman

Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0003-3036-2291
Laszlo Kocsis

Laboratory of Cellular Neurophysiology, Hungarian Academy of Sciences, Budapest, Hungary

Competing interests
The authors declare that no competing interests exist.
Etienne Herzog

Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Göttingen, Germany

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-0058-6959
Zoltan Nusser

Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary

For correspondence
nusser@koki.hu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0001-7004-4111
Robin Angus Silver

Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom

For correspondence
a.silver@ucl.ac.uk

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-5480-6638

Funding

Wellcome Trust (95667)

Robin Angus Silver

European Research Council (294667)

Robin Angus Silver

European Research Council (293681)

Zoltan Nusser

Magyar Tudományos Akadémia (Momentum Grant, Lendület, LP2012-29)

Zoltan Nusser

European Commission (LSHM-CT-2005-019055)

Zoltan Nusser
Robin Angus Silver

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Ethics

Animal experimentation: Animal experiments were conducted in strict accordance with the United Kingdom Home Office Animals Scientific Procedures Act of 1986, and approved by the UCL ethics review board. All mice were anaesthetized with ketamine or isoflurane during surgical procedures.

Copyright

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.