Abstract
The mouse somatosensory cortex is an excellent model to study the structural basis of cortical information processing, since it possesses anatomically recognizable domains that receive different thalamic inputs, which indicates spatial segregation of different processing tasks. In this work we examined three genetically labeled, non-overlapping subpopulations of GABAergic neurons: parvalbumin- (PV+), somatostatin- (SST+), and vasoactive intestinal polypeptide-expressing (VIP+) cells. Each of these subpopulations displayed a unique cellular distribution pattern across layers. In terms of columnar localization, the distribution of these three populations was not quantitatively different between barrel-related versus septal compartments in most layers. However, in layer IV (LIV), SST+, and VIP+, but not PV+ neurons preferred the septal compartment over barrels. The examined cell types showed a tendency toward differential distribution in supragranular and infragranular barrel-related versus septal compartments, too. Our data suggests that the location of GABAergic neuron cell bodies correlates with the spatial pattern of cortical domains receiving different kinds of thalamic input. Thus, at least in LIV, lemniscal inputs present a close spatial relation preferentially to PV+ cells whereas paralemniscal inputs target compartments in which more SST+ and VIP+ cells are localized. Our findings suggest pathway-specific roles for neocortical GABAergic neurons.
Highlights
The neocortex contains two main groups of neurons: the excitatory glutamatergic cells and the inhibitory GABAergic cells, which both are crucial for sensory information processing (Harris and Mrsic-Flogel, 2013)
The main question was, whether a compartmentassociated distribution of GABAergic neurons can be found? Our results show that laminar and columnar preferences obviously do exist for the soma locations of PV+, SST+, and vasoactive intestinal polypeptide (VIP)+ cells, only in layer IV (LIV) and only for SST+ and VIP+ cells, these differences reach statistical significance
These cells show a dominant location within the termination zones of the lemniscal thalamic projections (Chmielowska et al, 1989; Wimmer et al, 2010b), namely LIV and the layer Vb (LVb)/VI border and within the termination zone of paralemniscal thalamic projections (Wimmer et al, 2010b), namely layer Va (Figure 1A)
Summary
The neocortex contains two main groups of neurons: the excitatory glutamatergic cells and the inhibitory GABAergic cells, which both are crucial for sensory information processing (Harris and Mrsic-Flogel, 2013). These two groups are molecularly, morphologically and physiologically distinct. The parvalbumin (PV+), somatostatin (SST+), and vasoactive intestinal polypeptide (VIP+) expressing cells account for the majority of GABAergic neurons (roughly 40% PV, 30% SST, and 10–15% VIP) These three distinct classes show minimal overlap in all examined cortical areas (Pfeffer et al, 2013; Tremblay et al, 2016), and have diverse molecular, structural and electrophysiological features. We described the spatial distribution of these neuron types, in order to investigate their relationship to cortical compartments receiving different thalamic afferentation
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