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Channelrhodopsin-2-assisted circuit mapping of long-range callosal projections.

The functions of cortical areas depend on their inputs and outputs, but the detailed circuits made by long-range projections are unknown. We show that the light-gated channel channelrhodopsin-2 (ChR2) is delivered to axons in pyramidal neurons in vivo. In brain slices from ChR2-expressing mice, photostimulation of ChR2-positive axons can be transduced reliably into single action potentials. Combining photostimulation with whole-cell recordings of synaptic currents makes it possible to map circuits between presynaptic neurons, defined by ChR2 expression, and postsynaptic neurons, defined by targeted patching. We applied this technique, ChR2-assisted circuit mapping (CRACM), to map long-range callosal projections from layer (L) 2/3 of the somatosensory cortex. L2/3 axons connect with neurons in L5, L2/3 and L6, but not L4, in both ipsilateral and contralateral cortex. In both hemispheres the L2/3-to-L5 projection is stronger than the L2/3-to-L2/3 projection. Our results suggest that laminar specificity may be identical for local and long-range cortical projections.

Pubmed ID: 17435752


  • Petreanu L
  • Huber D
  • Sobczyk A
  • Svoboda K


Nature neuroscience

Publication Data

May 24, 2007

Associated Grants


Mesh Terms

  • Animals
  • Animals, Newborn
  • Axons
  • Brain Mapping
  • Corpus Callosum
  • Embryo, Mammalian
  • Female
  • Functional Laterality
  • In Vitro Techniques
  • Membrane Potentials
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Nerve Net
  • Neural Pathways
  • Patch-Clamp Techniques
  • Photic Stimulation
  • Pregnancy
  • Retinaldehyde
  • Rhodopsin
  • Somatosensory Cortex