Multi-synaptic boutons are a feature of CA1 hippocampal connections in the stratum oriens

Mark Rigby, Federico W. Grillo, Benjamin Compans, Guilherme Neves, Julia Gallinaro, Sophie Nashashibi, Sally Horton, Pedro M. Pereira Machado, Maria Alejandra Carbajal, Gema Vizcay-Barrena, Florian Levet, Jean Baptiste Sibarita, Angus Kirkland, Roland A. Fleck, Claudia Clopath, Juan Burrone*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


Excitatory synapses are typically described as single synaptic boutons (SSBs), where one presynaptic bouton contacts a single postsynaptic spine. Using serial section block-face scanning electron microscopy, we found that this textbook definition of the synapse does not fully apply to the CA1 region of the hippocampus. Roughly half of all excitatory synapses in the stratum oriens involved multi-synaptic boutons (MSBs), where a single presynaptic bouton containing multiple active zones contacted many postsynaptic spines (from 2 to 7) on the basal dendrites of different cells. The fraction of MSBs increased during development (from postnatal day 22 [P22] to P100) and decreased with distance from the soma. Curiously, synaptic properties such as active zone (AZ) or postsynaptic density (PSD) size exhibited less within-MSB variation when compared with neighboring SSBs, features that were confirmed by super-resolution light microscopy. Computer simulations suggest that these properties favor synchronous activity in CA1 networks.

Original languageEnglish
Article number112397
JournalCell Reports
Issue number5
Publication statusPublished - 30 May 2023


  • axon
  • connectome
  • CP: Neuroscience
  • dendrite
  • hippocampus
  • multi-synaptic bouton
  • network synchrony
  • synapse


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