Systematic heterogeneity of fractional vesicle pool sizes and release rates of hippocampal synapses

Biophys J. 2011 Feb 2;100(3):593-601. doi: 10.1016/j.bpj.2010.12.3706.


Hippocampal neurons in tissue culture develop functional synapses that exhibit considerable variation in synaptic vesicle content (20-350 vesicles). We examined absolute and fractional parameters of synaptic vesicle exocytosis of individual synapses. Their correlation to vesicle content was determined by activity-dependent discharge of FM-styryl dyes. At high frequency stimulation (30 Hz), synapses with large recycling pools released higher amounts of dye, but showed a lower fractional release compared to synapses that contained fewer vesicles. This effect gradually vanished at lower frequencies when stimulation was triggered at 20 Hz and 10 Hz, respectively. Live-cell antibody staining with anti-synaptotagmin-1-cypHer 5, and overexpression of synaptopHluorin as well as photoconversion of FM 1-43 followed by electron microscopy, consolidated the findings obtained with FM-styryl dyes. We found that the readily releasable pool grew with a power function with a coefficient of 2/3, possibly indicating a synaptic volume/surface dependency. This observation could be explained by assigning the rate-limiting factor for vesicle exocytosis at high frequency stimulation to the available active zone surface that is proportionally smaller in synapses with larger volumes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Artifacts
  • Endocytosis
  • Exocytosis
  • Fluorescent Dyes / metabolism
  • Hippocampus / cytology
  • Hippocampus / metabolism*
  • Hippocampus / ultrastructure
  • Kinetics
  • Microscopy, Fluorescence
  • Pyridinium Compounds / metabolism
  • Quaternary Ammonium Compounds / metabolism
  • Rats
  • Rats, Wistar
  • Surface Properties
  • Synaptic Vesicles / metabolism*
  • Synaptic Vesicles / ultrastructure
  • Time Factors


  • FM1 43
  • Fluorescent Dyes
  • Pyridinium Compounds
  • Quaternary Ammonium Compounds