Zw. Zhang et M. Deschenes, INTRACORTICAL AXONAL PROJECTIONS OF LAMINA-VI CELLS OF THE PRIMARY SOMATOSENSORY CORTEX IN THE RAT - A SINGLE-CELL LABELING STUDY, The Journal of neuroscience, 17(16), 1997, pp. 6365-6379
A sample of 84 neurons in lamina Via of rat somatosensory cortex (S1)
was juxtacellularly labeled with biocytin, and the axons of the neuron
s were traced, Three classes of cells were identified as corticothalam
ic, corticocortical, and local circuit neurons, Corticothalamic cells
(46%) are small, short pyramids projecting either to the ventral poste
romedial nucleus alone or to the posterior group as well. The former a
re in upper lamina Vl, have apical dendrites terminating in layer IV,
and have intracortical collaterals ascending to layer IV as a narrow c
olumn about the size of a barrel. The latter are in the lower half of
lamina VI, have apical dendrites terminating in layer V, and have a mo
re extensive network of collaterals terminating in the upper part of l
amina V. Corticothalamic cells do not project to distant cortical targ
ets through branching axons, Corticocortical cells (44%) are small, sh
ort pyramids, inverted or modified pyramids, or bipolar spiny neurons.
They send collaterals principally to infragranular layers of S1 and b
ranches to the second somatosensory cortex, the motor cortex, or the c
orpus callosum. Local circuit neurons (10%) are basket cells, concentr
ated in upper lamina VI, having smooth, beaded dendrites and a rich co
llateral network densely covered with varicosities in layers V and V1.
We conclude that (1) dendritic morphology and axonal arborizations of
corticothalamic cells relate to the projection target; (2) many appar
ently diverse layer VI cells project to other cortical fields; and (3)
lamina VI is a network for corticothalamic and corticocortical commun
ication.