In vivo synaptic recovery following optogenetic hyperstimulation

Proc Natl Acad Sci U S A. 2013 Aug 6;110(32):E3007-16. doi: 10.1073/pnas.1305679110. Epub 2013 Jul 22.


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.

Keywords: channelrhodopsin; chemical synapse; electron microscopy; synaptic vesicle recycling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Genetically Modified
  • Caenorhabditis elegans / genetics
  • Caenorhabditis elegans / metabolism
  • Caenorhabditis elegans / physiology
  • Caenorhabditis elegans Proteins / genetics
  • Caenorhabditis elegans Proteins / metabolism
  • Caenorhabditis elegans Proteins / physiology
  • Dynamins / genetics
  • Dynamins / metabolism
  • Dynamins / physiology
  • Endocytosis / genetics
  • Endocytosis / physiology
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Microscopy, Electron
  • Microscopy, Fluorescence
  • Motor Neurons / metabolism
  • Motor Neurons / physiology*
  • Mutation
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism
  • Nerve Tissue Proteins / physiology
  • Optogenetics / methods*
  • Phosphoric Monoester Hydrolases / genetics
  • Phosphoric Monoester Hydrolases / metabolism
  • Phosphoric Monoester Hydrolases / physiology
  • RNA Interference
  • Synaptic Transmission / physiology*
  • Synaptic Vesicles / metabolism
  • Synaptic Vesicles / physiology*
  • Synaptic Vesicles / ultrastructure
  • Time Factors


  • Caenorhabditis elegans Proteins
  • Luminescent Proteins
  • Nerve Tissue Proteins
  • synaptojanin
  • Phosphoric Monoester Hydrolases
  • Dyn-1 protein, C elegans
  • Dynamins