RESEARCH ARTICLE Physical determinants of vesicle mobility and supply at a central synapse Jason Seth Rothman1, Laszlo Kocsis2, Etienne Herzog3,4, Zoltan Nusser2*, Robin Angus Silver1* 1Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom; 2Laboratory of Cellular Neurophysiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary; 3Department of Molecular Neurobiology, Max Planck Institute of Experimental Medicine, Go¨ ttingen, Germany; 4Team Synapse in Cognition, Interdisciplinary Institute for Neuroscience, Universite´ de Bordeaux, UMR 5297, F-33000, Bordeaux, France 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 VGLUT1Venus 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, *For correspondence: nusser@ diffusion limits vesicle reloading during sustained high-frequency signalling. koki.hu (ZN);
[email protected] DOI: 10.7554/eLife.15133.001 (RAS) Competing interests: The authors declare that no competing interests exist.