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Cerebral Cortex Advance Access published online on September 11, 2008
Cerebral Cortex, doi:10.1093/cercor/bhn138
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

The Relation between Dendritic Geometry, Electrical Excitability, and Axonal Projections of L2/3 Interneurons in Rat Barrel Cortex

Moritz Helmstaedter1, Bert Sakmann1 and Dirk Feldmeyer2,3

1 Department of Cell Physiology, Max-Planck Institute for Medical Research, Jahnstraße 29, D-69120 Heidelberg, Germany, 2 Research Centre Jülich, Institute for Neuroscience and Biophysics, INB-3 Medicine, Leo-Brandt-Strasse, D-52425 Jülich, Germany, 3 Department of Psychiatry and Psychotherapy, RWTH Aachen University, Pauwelsstrasse 30, D-52074 Aachen, Germany

Address correspondence to Moritz Helmstaedter, Department of Cell Physiology, Max-Planck Institute for Medical Research, Jahnstr. 29, D-69120 Heidelberg, Germany. Email: moritz.helmstaedter{at}mpimf-heidelberg.mpg.de.

Interneurons in layer 2/3 (L2/3) of the somatosensory cortex show 4 types of axonal projection patterns with reference to the laminae and borders of columns in rat barrel cortex (Helmstaedter et al. 2008a). Here, we analyzed the dendritic geometry and electrical excitability of these interneurons. First, dendritic polarity, measured based on the insertion points of primary dendrites on the soma surface, yielded a continuous one-dimensional measure without a clustering of dendritic polarity types. Secondly, we analyzed polar and vertical distributions of dendritic length. A cluster analysis allowed the definition of 7 types of dendritic arborization. Thirdly, when dendritic polarity was related to the intrinsic electrical excitability we found that the ratio of frequency adaptation in trains of action potentials (APs) evoked by current injection was correlated with the number of primary dendrites. Numerical simulations of spiking patterns in L2/3 interneurons suggested that the number of primary dendrites could account for up to 50% of this correlation. Fourthly, dendritic arborization was not correlated with axonal projection, and axonal projection types could not be predicted by electrical excitability parameters. We conclude that 1) dendritic polarity is correlated to intrinsic electrical excitability, and 2) the axonal projection pattern represents an independent classifier of interneurons.

Key Words: barrel cortex • cluster analysis • dendrites • electrical excitability • GABAergic interneuron • layer 2/3 • simulation


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