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Original Research ARTICLE

Retrograde tracing with recombinant rabies virus reveals correlations between projection targets and dendritic architecture in layer 5 of mouse barrel cortex

DeLaine D. Larsen, Ian R. Wickersham and Edward M. Callaway^*

Systems Neurobiology Laboratories, The Salk Institute for Biological Studies, Neurosciences Graduate Program, University of California, San Diego, La Jolla, CA, USA

A recombinant rabies virus was used as a retrograde tracer to allow complete filling of the axonal and dendritic arbors of identified projection neurons in layer 5 of mouse primary somatosensory cortex (S1) in vivo. Previous studies have distinguished three types of layer 5 pyramids in S1: tall-tufted, tall-simple, and short. Layer 5 pyramidal neurons were retrogradely labeled from several known targets: contralateral S1, superior colliculus, and thalamus. The complete dendritic arbors of labeled cells were reconstructed to allow for unambiguous classification of cell type. We confirmed that the tall-tufted pyramids project to the superior colliculus and thalamus and that short layer 5 pyramidal neurons project to contralateral cortex, as previously described. We found that tall-simple pyramidal neurons contribute to corticocortical connections. Axonal reconstructions show that corticocortical projection neurons have a large superficial axonal arborization locally, while the subcortically projecting neurons limit axonal arbors to the deep layers. Furthermore, reconstructions of local axons suggest that tall-simple cell axons have extensive lateral spread while those of the short pyramids are more columnar. These differences were revealed by the ability to completely label dendritic and axonal arbors in vivo and have not been apparent in previous studies using labeling in brain slices.

Keywords:

local circuits, pyramidal neuron, axonal branching, barrel cortex, rabies virus, thalamus, superior colliculus

Citation:

Larsen DD, Wickersham IR and Callaway EM (2008). Retrograde tracing with recombinant rabies virus reveals correlations between projection targets and dendritic architecture in layer 5 of mouse barrel cortex. Front. Neural Circuits 1:5. doi: 10.3389/neuro.04.005.2007

Received:

24 October 2007;

Paper pending published:

26 November 2007;

Accepted:

11 February 2008;

Published online:

28 March 2008 .

Edited by:

Rafael Yuste, Columbia University, USA

Reviewed by:

Michael Brecht, Humboldt University of Berlin, Germany
Dmitri ' Mitya ' Chklovskii, Cold Spring Harbor Laboratory, USA

© 2008 Larsen, Wickersham and Callaway. This is an open-access article subject to an exclusive license agreement between the authors and the Frontiers Research Foundation, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are credited.

*Correspondence:

Edward M. Callaway, Systems Neurobiology Laboratories, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA; Neurosciences Graduate Program, University of California, San Diego, La Jolla, CA 92039, USA. e-mail: callaway@salk.edu