Release probability of hippocampal glutamatergic terminals scales with the size of the active zone

Nat Neurosci. 2012 Jun 10;15(7):988-97. doi: 10.1038/nn.3137.


Cortical synapses have structural, molecular and functional heterogeneity; our knowledge regarding the relationship between their ultrastructural and functional parameters is still fragmented. Here we asked how the neurotransmitter release probability and presynaptic [Ca(2+)] transients relate to the ultrastructure of rat hippocampal glutamatergic axon terminals. Two-photon Ca(2+) imaging-derived optical quantal analysis and correlated electron microscopic reconstructions revealed a tight correlation between the release probability and the active-zone area. Peak amplitude of [Ca(2+)] transients in single boutons also positively correlated with the active-zone area. Freeze-fracture immunogold labeling revealed that the voltage-gated calcium channel subunit Cav2.1 and the presynaptic protein Rim1/2 are confined to the active zone and their numbers scale linearly with the active-zone area. Gold particles labeling Cav2.1 were nonrandomly distributed in the active zones. Our results demonstrate that the numbers of several active-zone proteins, including presynaptic calcium channels, as well as the number of docked vesicles and the release probability, scale linearly with the active-zone area.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials / physiology*
  • Animals
  • Calcium Channels, N-Type / metabolism
  • Calcium Channels, N-Type / ultrastructure
  • Hippocampus / metabolism*
  • Hippocampus / ultrastructure
  • Male
  • Presynaptic Terminals / metabolism*
  • Presynaptic Terminals / ultrastructure
  • Random Allocation
  • Rats
  • Rats, Wistar
  • Synaptic Vesicles / metabolism*


  • Calcium Channels, N-Type
  • voltage-dependent calcium channel (P-Q type)