Specificity of synaptic connectivity between layer 1 inhibitory interneurons and layer 2/3 pyramidal neurons in the rat neocortex

Cereb Cortex. 2011 Aug;21(8):1818-26. doi: 10.1093/cercor/bhq257. Epub 2011 Jan 10.


Understanding the structure and function of the neocortical microcircuit requires a description of the synaptic connectivity between identified neuronal populations. Here, we investigate the electrophysiological properties of layer 1 (L1) neurons of the rat somatosensory neocortex (postnatal day 24-36) and their synaptic connectivity with supragranular pyramidal neurons. The active and passive properties of visually identified L1 neurons (n = 266) suggested division into 4 groups according to the Petilla classification scheme with characteristics of neurogliaform cells (NGFCs) (n = 72), classical-accommodating (n = 137), fast-spiking (n = 23), and burst-spiking neurons (n = 34). Anatomical reconstructions of L1 neurons supported the existence of 4 major neuronal groups. Multiparameter unsupervised cluster analysis confirmed the existence of 4 groups, revealing a high degree of similarity with the Petilla scheme. Simultaneous recordings between synaptically connected L1 neurons and L2/3 pyramidal neurons (n = 384) demonstrated neuronal class specificity in both excitatory and inhibitory connectivity and the properties of synaptic potentials. Notably, all groups of L1 neurons received monosynaptic excitatory input from L2/3 pyramidal neurons (n = 33), with the exception of NGFCs (n = 68 pairs tested). In contrast, NGFCs strongly inhibited L2/3 pyramidal neurons (n = 12 out 27 pairs tested). These data reveal a high specificity of excitatory and inhibitory connections in the superficial layers of the neocortex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Communication / physiology*
  • Interneurons / classification
  • Interneurons / cytology
  • Interneurons / physiology*
  • Neocortex / cytology
  • Neocortex / physiology*
  • Neural Inhibition / physiology*
  • Neural Pathways / cytology
  • Neural Pathways / physiology
  • Organ Culture Techniques
  • Pyramidal Cells / cytology
  • Pyramidal Cells / physiology*
  • Rats
  • Rats, Wistar
  • Somatosensory Cortex / cytology
  • Somatosensory Cortex / physiology*
  • Synapses / physiology*
  • Synaptic Transmission / physiology