Abstract
The rat primary somatosensory cortex (S1) is remarkable for its conspicuous vertical compartmentalization in barrels and septal columns, which are additionally stratified in horizontal layers. Whereas excitatory neurons from each of these compartments perform different types of processing, the role of interneurons is much less clear. Among the numerous types of GABAergic interneurons, those producing nitric oxide (NO) are especially puzzling, since this gaseous messenger can modulate neural activity, synaptic plasticity, and neurovascular coupling. We used a quantitative morphological approach to investigate whether nitrergic interneurons, which might therefore be considered both as NO volume diffusers and as elements of local circuitry, display features that could relate to barrel cortex architecture. In fixed brain sections, nitrergic interneurons can be revealed by histochemical processing for NADPH-diaphorase (NADPHd). Here, the dendritic arbors of nitrergic neurons from different compartments of area S1 were 3D reconstructed from serial 200 μm thick sections, using 100x objective and the Neurolucida system. Standard morphological parameters were extracted for all individual arbors and compared across columns and layers. Wedge analysis was used to compute dendritic orientation indices. Supragranular (SG) layers displayed the highest density of nitrergic neurons, whereas layer IV contained nitrergic neurons with largest soma area. The highest nitrergic neuronal density was found in septa, where dendrites were previously characterized as more extense and ramified than in barrels. Dendritic arbors were not confined to the boundaries of the column nor layer of their respective soma, being mostly double-tufted and vertically oriented, except in SG layers. These data strongly suggest that nitrergic interneurons adapt their morphology to the dynamics of processing performed by cortical compartments.
Highlights
The cortical nitrergic system is composed of inhibitory GABAergic neurons that express nitric oxide synthase (NOS) (Bredt et al, 1991; Dawson et al, 1991; Hope et al, 1991; Yan and Garey, 1997; Kubota et al, 2011), the enzyme responsible for synthesis of nitric oxide (NO)
NEUROPIL STAINING AND MORPHOLOGICAL ASPECTS OF NITRERGIC NEURONS IN RAT PRIMARY SOMATOSENSORY CORTEX In coronal sections of rat cortex, area S1 was identified due to the strong NADPHd-reactive neuropil characteristic of layer IV barrels, intercalated with less reactive septa (Figure 1). This pattern was found in the expected position for the barrel fields (Zilles and Wree, 1985), as previously described with this technique in tangential sections (Franca and Volchan, 1995)
The border between layers II and III could not be reliably identified by means of NADPHd histochemistry
Summary
The cortical nitrergic system is composed of inhibitory GABAergic neurons that express nitric oxide synthase (NOS) (Bredt et al, 1991; Dawson et al, 1991; Hope et al, 1991; Yan and Garey, 1997; Kubota et al, 2011), the enzyme responsible for synthesis of nitric oxide (NO). NO is an unusual neurotransmitter (Bredt et al, 1991; Dawson and Snyder, 1994), involved in a wide range of physiological and pathological events in the central nervous system, such as modulation of synaptic transmission and neurotoxicity (Wallace et al, 1996; Estevez et al, 1998; see Calabrese et al, 2007; Garthwaite, 2008 for review). Activation of NOS is one of the factors that leads to vasodilation following neuronal activation, leading to an increase in local cerebral blood flow (Drake and Iadecola, 2007; Cauli and Hamel, 2010). Nitrergic neurons are part of the intrinsic neuronal circuitry They release neuropeptide Y (NPY)—a potent vasoconstrictor—on blood vessels located distal to the cell body. Distal release of NPY may restrict the NO-induced vasodilation to the micro region around the Frontiers in Neural Circuits www.frontiersin.org
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