Empirical assessment of synapse numbers in primate neocortex

Peter R. Mouton, Donald L. Price, Lary C. Walker

Research output: Contribution to journalArticlepeer-review


Reliable methods are needed to assess the impact of synaptic loss on brain function. In this empirical study we demonstrate a novel and efficient method using immunocytochemistry (ICC) and modern stereological techniques to quantify synapses in neocortex of adult primates (Macaca fascicularis). Systematic-uniform-random sections through forebrain from two 10-year-old monkeys were immunostained for estimation of synaptophysin-immunoreactive (synaptophysin-IR) presynaptic boutons (synapses). Adjacent sections were stained with cresyl violet for estimation of total number of neuronal cell bodies. The unbiased Cavalieri method was used to estimate total forebrain and neocortical volumes to a high level of precision (coefficient of error (CE) ≤ 0.10)). Synapse-to-neuron ratios varied from 860 in frontal cortex to 2300 in parietal-temporal cortex. The combination of Cavalieri and optical disector methods provided a direct means of estimating ≃ 1.25 trillion (x 1012) total synaptophysin-immunopositive boutons and ≃ 1.01 billion (x 109) cell bodies in neocortex, with low CEs (0.12). Time required to make precise estimates of total neocortical and forebrain volumes and total numbers of synapses and neurons in neocortex was ≃2-3 h per case from stained sections. The approach is a direct and efficient technique to quantify total synapse and neuron numbers within a defined brain structure.

Original languageEnglish (US)
Pages (from-to)119-126
Number of pages8
JournalJournal of Neuroscience Methods
Issue number2
StatePublished - Aug 22 1997


  • Cavalieri principle
  • Neocortex
  • Optical disector
  • Synapses
  • Synaptophysin
  • Unbiased stereology

ASJC Scopus subject areas

  • Neuroscience(all)


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