title: In vivo synaptic recovery following optogenetic hyperstimulation.
abstract: Local recycling of synaptic vesicles (SVs) allows neurons to sustain transmitter release. Extreme activity (e.g., during seizure) may exhaust synaptic transmission and, in vitro, induces bulk endocytosis to recover SV membrane and proteins; how this occurs in animals is unknown. Following optogenetic hyperstimulation of Caenorhabditis elegans motoneurons, we analyzed synaptic recovery by time-resolved behavioral, electrophysiological, and ultrastructural assays. Recovery of docked SVs and of evoked-release amplitudes (indicating readily-releasable pool refilling) occurred within ∼8-20 s (τ = 9.2 s and τ = 11.9 s), whereas locomotion recovered only after ∼60 s (τ = 20 s). During ∼11-s stimulation, 50- to 200-nm noncoated vesicles ("100nm vesicles") formed, which disappeared ∼8 s poststimulation, likely representing endocytic intermediates from which SVs may regenerate. In endophilin, synaptojanin, and dynamin mutants, affecting endocytosis and vesicle scission, resolving 100nm vesicles was delayed (>20 s). In dynamin mutants, 100nm vesicles were abundant and persistent, sometimes continuous with the plasma membrane; incomplete budding of smaller vesicles from 100nm vesicles further implicates dynamin in regenerating SVs from bulk-endocytosed vesicles. Synaptic recovery after exhaustive activity is slow, and different time scales of recovery at ultrastructural, physiological, and behavioral levels indicate multiple contributing processes. Similar processes may jointly account for slow recovery from acute seizures also in higher animals.
authors.affiliation: European Neuroscience Institute and Center for Molecular Physiology of the Brain, Georg August University, D-37077 Göttingen, Germany.
authors.forename: Maike
authors.initials: M
authors.lastname: Kittelmann
authors.forename: Jana F
authors.initials: JF
authors.lastname: Liewald
authors.forename: Jan
authors.initials: J
authors.lastname: Hegermann
authors.forename: Christian
authors.initials: C
authors.lastname: Schultheis
authors.forename: Martin
authors.initials: M
authors.lastname: Brauner
authors.forename: Wagner
authors.initials: W
authors.lastname: Steuer Costa
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wabnig
authors.forename: Stefan
authors.initials: S
authors.lastname: Eimer
authors.forename: Alexander
authors.initials: A
authors.lastname: Gottschalk
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D034281:Dynamins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D004705:Endocytosis / Q000235:genetics / Q000502:physiology; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009046:Motor Neurons / Q000378:metabolism / Q000502:physiology*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D062308:Optogenetics / Q000379:methods*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D034622:RNA Interference; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D013997:Time Factors
chemical_list: D029742:Caenorhabditis elegans Proteins; D008164:Luminescent Proteins; D009419:Nerve Tissue Proteins; C097702:synaptojanin; D010744:Phosphoric Monoester Hydrolases; C511792:Dyn-1 protein, C elegans; D034281:Dynamins
keywords: channelrhodopsin; chemical synapse; electron microscopy; synaptic vesicle recycling