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

Nature Neuroscience volume 10, pages 663668 (2007) | Download Citation

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Abstract

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.

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Acknowledgements

We thank members of our laboratory for discussion, D. Chklovskii, E. Chiappe, G. Shepherd and J. Magee for comments on the manuscript, and T. O'Connor for software development. This work was supported by the Howard Hughes Medical Institute, the US National Institute of Health and the Swiss National Science Foundation (D.H.).

Author information

Affiliations

  1. Howard Hughes Medical Institute, Janelia Farm Research Campus, 19700 Helix Drive, Ashburn, Virginia 20147, USA, and Cold Spring Harbor Laboratory, 1 Bungtown Rd., Cold Spring Harbor, New York 11724, USA.

    • Leopoldo Petreanu
    • , Daniel Huber
    • , Aleksander Sobczyk
    •  & Karel Svoboda

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Contributions

L.P. and K.S. conceived and designed the experiments, analyzed the data and wrote the manuscript. L.P., D.H. and A.S. conducted the experiments. K.S. provided reagents, analysis tools and financial support.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Karel Svoboda.

Supplementary information

PDF files

  1. 1.

    Supplementary Fig. 1

    ChR2 photoexcitation in L2/3 neurons.

  2. 2.

    Supplementary Fig. 2

    Excitation of a ChR2-positive L2/3 cell at different laser powers.

  3. 3.

    Supplementary Fig. 3

    The number of excited axons increases with laser power.

  4. 4.

    Supplementary Fig. 4

    ChR2-negative cells do not respond to repeated laser photostimulation.

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DOI

https://doi.org/10.1038/nn1891

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