|In primates, little is known about intrinsic electrophysiological
properties of neocortical neurons and their morphological correlates. To
classify inhibitory interneurons in layers 2-3 of monkey dorsolateral prefrontal
cortex, we employed whole cell voltage recordings and intracellular labeling
in slice preparations with subsequent morphological reconstructions. Regular-spiking
pyramidal cells were also included in the sample. As shown in the Figure,
regular-spiking neurons (RSN) display low input resistance and require the
largest amplitude of depolarization current to reach action potential threshold.
In contrast, intermediate-spiking neurons (ISN) have the largest input resistance
and require the lowest amplitude of depolarization current to reach action
potential threshold. Fast-spiking neurons (FSN) display properties intermediate
between RSN and ISN. As shown in panel D, monoexponential curve fittings
to the first hyperpolarizing sweeps demonstrate longest, intermediate and
shortest time constant in the RSN, ISN and FSN, respectively. Using cluster
analysis as a multivariate exploratory technique, morphological types of
neurons were mapped on these physiological clusters. The cluster of RSN
contained all pyramidal cells, whereas the ISN and FSN clusters consisted
exclusively of interneurons. The cluster of FSN contained all of the chandelier
cells and the majority of local, medium and wide arbor (basket) interneurons.
The cluster of ISN predominantly consisted of cells with the morphology
of neurogliaform or vertically oriented (double bouquet) interneurons. Thus,
a quantitative approach enabled us to demonstrate that intrinsic electrophysiological
properties of neurons in the monkey prefrontal cortex define distinct cell
types, which also display distinct morphologies.
LS, Zaitsev AV, Czanner G, Kröner S, González-Burgos G, Povysheva
NV, Iyengar S, Barrionuevo G and Lewis DA: Cluster analysis-based physiological
classification and morphological properties of inhibitory neurons in layers
2-3 of monkey dorsolateral prefrontal cortex. J. Neurophysiol 94: 3009-3022, 2005.