Glutamatergic nonpyramidal neurons from neocortical layer VI and their comparison with pyramidal and spiny stellate neurons.
Journal of Neurophysiology. 2009-02-01; 101(2): 641-654
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1. J Neurophysiol. 2009 Feb;101(2):641-54. doi: 10.1152/jn.91094.2008. Epub 2008 Dec
Glutamatergic nonpyramidal neurons from neocortical layer VI and their comparison
with pyramidal and spiny stellate neurons.
Andjelic S(1), Gallopin T, Cauli B, Hill EL, Roux L, Badr S, Hu E, Tamás G,
(1)NPA CNRS UMR 710, UPMC, 9 quai St Bernard, 75005 Paris, France.
The deeper part of neocortical layer VI is dominated by nonpyramidal neurons,
which lack a prominent vertically ascending dendrite and predominantly establish
corticocortical connections. These neurons were studied in rat neocortical slices
using patch-clamp, single-cell reverse transcription-polymerase chain reaction,
and biocytin labeling. The majority of these neurons expressed the vesicular
glutamate transporter but not glutamic acid decarboxylase, suggesting that a high
proportion of layer VI nonpyramidal neurons are glutamatergic. Indeed, they
exhibited numerous dendritic spines and established asymmetrical synapses. Our
sample of glutamatergic nonpyramidal neurons displayed a wide variety of
somatodendritic morphologies and a subset of these cells expressed the Nurr1
mRNA, a marker for ipsilateral, but not commissural corticocortical projection
neurons in layer VI. Comparison with spiny stellate and pyramidal neurons from
other layers showed that glutamatergic neurons consistently exhibited a low
occurrence of GABAergic interneuron markers and regular spiking firing patterns.
Analysis of electrophysiological diversity using unsupervised clustering
disclosed three groups of cells. Layer V pyramidal neurons were segregated into a
first group, whereas a second group consisted of a subpopulation of layer VI
neurons exhibiting tonic firing. A third heterogeneous cluster comprised spiny
stellate, layer II/III pyramidal, and layer VI neurons exhibiting adaptive
firing. The segregation of layer VI neurons in two different clusters did not
correlate either with their somatodendritic morphologies or with Nurr1
expression. Our results suggest that electrophysiological similarities between
neocortical glutamatergic neurons extend beyond layer positioning,
somatodendritic morphology, and projection specificity.
PMID: 19052106 [Indexed for MEDLINE]