Viral tracing identifies distributed columnar organization in the olfactory bulb

doi:10.1073/pnas.0602032103

Viral tracing identifies distributed columnar organization in the olfactory bulb

Departments of *Neurobiology and
^‡Neurosurgery, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06510

Edited by Dale Purves, Duke University Medical Center, Durham, NC, and approved June 26, 2006 (received for review March 17, 2006)

Abstract

Olfactory sensory neurons converge onto glomeruli in the olfactory bulb (OB) to form modular information processing units. Similar input modules are organized in translaminar columns for other sensory modalities. It has been less clear in the OB whether the initial modular organization relates to a columnar structure in the deeper layers involved in local circuit processing. To probe synaptic connectivity in the OB, we injected a retrograde-specific strain of the pseudorabies virus into the rat OB and piriform cortex. The viral-staining patterns revealed a striking columnar organization that extended across all layers of the OB from the glomeruli to the deep granule cell layer. We hypothesize that the columns represent an extension of the glomerular unit. Specific patterning was observed, suggesting selective, rather than distance-dependent, center-surround connectivity. The results provide a previously undescribed basis for interpreting the synaptic connections between mitral and granule cells within the context of a columnar organization in the OB and have implications for olfactory coding and network organization.

Footnotes

^†To whom correspondence should be addressed. E-mail: david.willhite{at}yale.edu
Author contributions: D.C.W. designed research; D.C.W., K.T.N., and A.V.M. performed research; D.C.W., C.A.G., G.M.S., and W.R.C. analyzed data; and D.C.W. and G.M.S. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Abbreviations

GCL,

granule cell layer;

LOT,

lateral olfactory tract;

OB,

olfactory bulb;

PRV,

pseudorabies virus;

SVZ,

subventricular zone.