Cerebral Cortex Advance Access originally published online on July 26, 2007
Cerebral Cortex 2008 18(4):876-889; doi:10.1093/cercor/bhm126
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Subcolumnar Dendritic and Axonal Organization of Spiny Stellate and Star Pyramid Neurons within a Barrel in Rat Somatosensory Cortex
Department of Cell Physiology, Max-Planck-Institute for Medical Research, Jahnstr. 29, 69120 Heidelberg, Germany, 1 Present address: Institut für Physiologie der Ludwig-Maximilians-Universität München, Pettenkoferstr. 12, 80336 München, Germany, 2 Present address: Institute for Physiology, Bern University, Bühlplatz 5, 3012 Bern, Switzerland
Address correspondence to Dr Veronica Egger, Institut für Physiologie der LMU, Pettenkoferstr. 12, 80336 München, Germany. Email: V.Egger{at}lmu.de.
Excitatory neurons at the level of cortical layer 4 in the rodent somatosensory barrel field often display a strong eccentricity in comparison with layer 4 neurons in other cortical regions. In rat, dendritic symmetry of the 2 main excitatory neuronal classes, spiny stellate and star pyramid neurons (SSNs and SPNs), was quantified by an asymmetry index, the dendrite-free angle. We carefully measured shrinkage and analyzed its influence on morphological parameters. SSNs had mostly eccentric morphology, whereas SPNs were nearly radially symmetric. Most asymmetric neurons were located near the barrel border. The axonal projections, analyzed at the level of layer 4, were mostly restricted to a single barrel except for those of 3 interbarrel projection neurons. Comparing voxel representations of dendrites and axon collaterals of the same neuron revealed a close overlap of dendritic and axonal fields, more pronounced in SSNs versus SPNs and considerably stronger in spiny L4 neurons versus extragranular pyramidal cells. These observations suggest that within a barrel dendrites and axons of individual excitatory cells are organized in subcolumns that may confer receptive field properties such as directional selectivity to higher layers, whereas the interbarrel projections challenge our view of barrels as completely independent processors of thalamic input.
Key Words: cortical column • dendritic symmetry • interbarrel projection • intrabarrel confinement • minicolumn • shrinkage
T.N. performed the measurements on tissue shrinkage and R.M.B. contributed the reconstructions of spiny layer 4 cells filled in vivo and substantial editorial input.
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