A gradual depth-dependent change in connectivity features of supragranular pyramidal cells in rat barrel cortex

Abstract

Recent experimental evidence suggests a finer genetic, structural and functional subdivision of the layers which form a cortical column. The classical layer II/III (LII/III) of rodent neocortex integrates ascending sensory information with contextual cortical information for behavioral read-out. We systematically investigated to which extent regular-spiking supragranular pyramidal neurons, located at different depths within the cortex, show different input–output connectivity patterns. Combining glutamate uncaging with whole-cell recordings and biocytin filling, we revealed a novel cellular organization of LII/III: (1) “Lower LII/III” pyramidal cells receive a very strong excitatory input from lemniscal LIV and much fewer inputs from paralemniscal LVa. They project to all layers of the home column, including a feedback projection to LIV, whereas transcolumnar projections are relatively sparse. (2) “Upper LII/III” pyramidal cells also receive their strongest input from LIV, but in addition, a very strong and dense excitatory input from LVa. They project extensively to LII/III as well as LVa and Vb of their home and neighboring columns. (3) “Middle LII/III” pyramidal cell shows an intermediate connectivity phenotype that stands in many ways in between the features described for lower versus upper LII/III. “Lower LII/III” intracolumnarly segregates and transcolumnarly integrates lemniscal information, whereas “upper LII/III” seems to integrate lemniscal with paralemniscal information. This suggests a fine-grained functional subdivision of the supragranular compartment containing multiple circuits without any obvious cytoarchitectonic, other structural or functional correlate of a laminar border in rodent barrel cortex.

NKCC-1 mediated Cl− uptake in immature CA3 pyramidal neurons is sufficient to compensate phasic GABAergic inputs

“…Data was corrected for tissue shrinkage after importing to the NEURON environment. For this purpose we used the values suggested by Staiger et al 60 and expanded the x-/y-dimensions by 12.5% and the z-dimension by 50%.…”

An Unexpected Dependence of Cortical Depth in Shaping Neural Responsiveness and Selectivity in Mouse Visual Cortex

“…Functional properties may vary across cells located at different depths within layer 2/3 in other sensory systems as well. Studies in the somatosensory and auditory cortices of mice have described differences in layer 2 and layer 3 in terms of their response properties as well as in their neuronal cell types and connectivity (Bureau et al, 2006;Winkowski and Kanold, 2013;Staiger et al, 2015;Meng et al, 2017). This suggests that there may be a common principle of systematic differences between layer 2 and layer 3 across the primary sensory cortices in mice and that the common practice of lumping these layers together may be problematic in certain cases.…”

Human cortical expansion involves diversification and specialization of supragranular intratelencephalic-projecting neurons

“…The supragranular cortex in human has been historically divided into layer 2 (L2) and 3 (with further subdivision of L3 depending on the cortical area), whereas such distinctions are not possible in mouse cortex, where supragranular cortex is referred to as layer 2/3 (L2/3). At the cellular level, rodent L2/3 pyramidal neurons form a relatively homogeneous population based on electrophysiological and morphological properties 1,2,7 , whereas in primates there is clear heterogeneity of neuron density, size, morphology, electrophysiology, and gene expression as a function of cortical depth and projection target 8,9,10,11,12,4,13,14,15 . For example two main anatomical types have been described in human that differ in their dendritic morphology (slender-versus profuse-tufted 13 ).…”