Morphometric analysis of the columnar innervation domain of neurons connecting layer 4 and layer 2/3 of juvenile rat barrel cortex

Cereb Cortex. 2003 Oct;13(10):1051-63. doi: 10.1093/cercor/13.10.1051.


We have investigated the dendritic and axonal morphology of connected pairs of L4 spiny neurons and L2/3 pyramidal cells in rat barrel cortex. The 'projection' field of the axons of L4 spiny neurons in layers 2/3, 4 and 5 has a width of 400-500 microm thereby defining an anatomical barrel-column. In layer 2/3, the averaged axonal 'projection' field of L4 spiny neurons together with the dendritic 'receptive' field of the connected L2/3 pyramidal cells form a mostly column-restricted anatomical L4-to-L2/3 'innervation domain' that extends 300-400 microm and includes mostly basal dendrites. In the L4-to-L2/3 innervation domain a single L4 spiny neuron contacts approximately 300-400 pyramidal cells while in the L4-to-L4 innervation domain it contacts approximately 200 other L4 spiny neurons. Similarly approximately 300-400 L4 spiny neurons converge onto a single pyramidal cell and approximately 200 L4 spiny neurons innervate another L4 spiny neuron. The L2/3 pyramidal cell axon has a vertical projection field spanning all cortical layers, and a long-range horizontal field in layers 2/3 (width 1,100-1,200 microm) and 5 (700-800 microm) projecting across column borders. The results suggest that the flow of excitation within a barrel-column is determined by the largely columnar confinement of the L4-to-L4 and L4-to-L2/3 innervation domains. A whisker deflection activates approximately 140 L4 spiny neurons that will generate EPSPs in most barrel-related L2/3 pyramidal cells of a principal whisker column. The translaminar synaptic transmission to layer 2/3 and the axonal projection fields of L2/3 pyramidal cells are the major determinants of the dynamic, multi-columnar map in which a single whisker deflection is represented in the cortex.

MeSH terms

  • Age Factors
  • Animals
  • Axons / physiology
  • Axons / ultrastructure
  • Cerebral Cortex / cytology*
  • Cerebral Cortex / physiology
  • Dendrites / physiology
  • Dendrites / ultrastructure
  • Excitatory Postsynaptic Potentials / physiology
  • Nerve Net / cytology*
  • Nerve Net / physiology
  • Neurons / cytology*
  • Neurons / physiology
  • Pyramidal Cells / cytology
  • Pyramidal Cells / physiology
  • Rats
  • Rats, Wistar