Number and Laminar Distribution of Neurons in a Thalamocortical Projection Column of Rat Vibrissal Cortex

Abstract

This is the second article in a series of three studies that investigate the anatomical determinants of thalamocortical (TC) input to excitatory neurons in a cortical column of rat primary somatosensory cortex (S1). Here, we report the number and distribution of NeuN-positive neurons within the C2, D2, and D3 TC projection columns in P27 rat somatosensory barrel cortex based on an exhaustive identification of 89 834 somata in a 1.15 mm3 volume of cortex. A single column contained 19 109 ± 444 neurons (17 560 ± 399 when normalized to a standard-size projection column). Neuron density differences along the vertical column axis delineated “cytoarchitectonic” layers. The resulting neuron numbers per layer in the average column were 63 ± 10 (L1), 2039 ± 524 (L2), 3735 ± 905 (L3), 4447 ± 439 (L4), 1737 ± 251 (L5A), 2235 ± 99 (L5B), 3786 ± 168 (L6A), and 1066 ± 170 (L6B). These data were then used to derive the layer-specific action potential (AP) output of a projection column. The estimates confirmed previous reports suggesting that the ensembles of spiny L4 and thick-tufted pyramidal neurons emit the major fraction of APs of a column. The number of APs evoked in a column by a sensory stimulus (principal whisker deflection) was estimated as 4441 within 100 ms post-stimulus.

Inhibitory interneurons in a cortical column form hot zones of inhibition in layers 2 and 5A

“…These data also allowed us to investigate the IN distribution in the tangential plane further. The number and distribution of all neurons in these three columns have been reported previously (21). Fig.…”

“…1A). We had found previously that the overall epifluorescence of tissue stained against glutamate decarboxylase 67 (GAD67) showed barrelrelated patches in L4 (corresponding to a high density of GAD67-positive boutons) and that these were aligned with the patches of thalamic afferents originating from the ventral posterior medial nucleus (21) (Fig. S1A).…”

“…2 A and C). The delineation of lateral column borders by NeuNpositive soma density was not observed in supra-or infragranular layers (21) (Fig. 2C).…”

“…All the slices contained the center of D2 (n = 5) and either C2 (n = 3) or E2 (n = 2). Markers were manually placed in somata of neurons and INs [details, especially the correction for doublecounting between slices, are discussed in the article by Meyer et al (21) and SI Materials and Methods]. Fig.…”

Mapping somatosensory connectivity in adult mice using diffusion MRI tractography and super-resolution track density imaging

“…Previous studies of the rodent somatosensory pathway have provided greater understanding of brain connectivity; however collecting micro-circuit information is extremely time consuming (Egger et al, 2012;Meyer et al, 2010;Oberlaender et al, 2012;Tsai et al, 2009;Wimmer et al, 2010). Here, we highlight the use of TDI to expedite whole brain connectivity data informing both structure and connectivity in mice at the mesoscopic (20µm) level.…”