Long‐range connectivity of mouse primary somatosensory barrel cortex

Abstract

The primary somatosensory barrel cortex processes tactile vibrissae information, allowing rodents to actively perceive spatial and textural features of their immediate surroundings. Each whisker on the snout is individually represented in the neocortex by an anatomically identifiable 'barrel' specified by the segregated termination zones of thalamocortical axons of the ventroposterior medial nucleus, which provide the primary sensory input to the neocortex. The sensory information is subsequently processed within local synaptically connected neocortical microcircuits, which have begun to be investigated in quantitative detail. In addition to these local synaptic microcircuits, the excitatory pyramidal neurons of the barrel cortex send and receive long-range glutamatergic axonal projections to and from a wide variety of specific brain regions. Much less is known about these long-range connections and their contribution to sensory processing. Here, we review current knowledge of the long-range axonal input and output of the mouse primary somatosensory barrel cortex. Prominent reciprocal projections are found between primary somatosensory cortex and secondary somatosensory cortex, motor cortex, perirhinal cortex and thalamus. Primary somatosensory barrel cortex also projects strongly to striatum, thalamic reticular nucleus, zona incerta, anterior pretectal nucleus, superior colliculus, pons, red nucleus and spinal trigeminal brain stem nuclei. These long-range connections of the barrel cortex with other specific cortical and subcortical brain regions are likely to play a crucial role in sensorimotor integration, sensory perception and associative learning.

Behaviour-dependent recruitment of long-range projection neurons in somatosensory cortex

“…For the construction of the pAAV-EF1a-YCNano140 viral construct, a YC-Nano140 insert with 59 BamHI and 39 EcoRI restriction sites was generated by polymerase chain reaction (PCR) amplification from a pcDNA3-YC-Nano140 vector 8 and subcloned into an pAAV-EF1a-dioeYFP plasmid 31 . The pAAV-pgk-Cre construct has been described previously 3 . Recombinant serotype 6 AAV particles were produced by co-transfecting AAV-293 cells with the shuttle plasmid and the pDP6 packaging plasmid.…”

“…In the whisker region of S1 (also known as the barrel cortex), layer 2/3 (L2/3) pyramidal neurons send direct projections to S2 and M1 in a generally non-overlapping manner [3][4][5][6] . We used a combination of viralbased and synthetic retrograde tracers to label uniquely these longrange projection neurons ( Fig.…”

“…1). Using adult transgenic Cre-dependent tdTomato reporter mice 7 , we injected a retrograde-infecting adeno-associated virus (AAV, serotype 6) expressing Cre recombinase (AAV6-Cre) 3 into S2 to induce long-term tdTomato expression in S2P neurons, later visualized in vivo (Fig. 1b and Supplementary Fig.…”

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

“…The structural composition and connectivity of the "whisker pathways" has been described using 2D histologic and functional activation methods. Network tracking techniques include lesion studies, (Killackey and Fleming, 1985;Killackey and Leshin, 1975); carbocyanine dyes (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine Perchlorate; DiI, DiA) (Kivrak and Erzurumlu, 2013;Seehaus et al, 2013) and myelin staining (Barrera et al, 2012); these techniques are also complemented by Lenti and Adeno-associated viral vector expression of fluorescent proteins (Aronoff et al, 2010;Dittgen et al, 2004;Wimmer et al, 2010). A range of macroscopic to microscopic functional connectivity mapping techniques include functional MRI (Kim et al, 2012;Yang et al, 1996), 2-photon imaging of electrical activity using voltage-sensitive dyes (Petersen et al, 2003a;Petersen et al, 2003b) and channelrhodopsins to map neuronal connectivity have also been conducted (Paz et al, 2011;Petreanu et al, 2007).…”

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“…From S1, information is sent simultaneously to the secondary somatosensory area (S2), the parietal ventral area (PV), the parietal rhinal area (PR), and the contralateral S1 (S1c) (Aronoff et al, 2010) (Krubitzer and Kaas, 1990;Fabri and Burton, 1991;Krubitzer et al, 1995;Disbrow et al, 2000;Remple et al, 2003;Ferezou et al, 2006;Henry et al, 2006; where it is integrated spatiotemporally (Zhu et al, 2007). Similar to S1, areas S2 and PV are organized topographically, with a complete representation of the contralateral half of the body and also receive direct thalamocortical inputs (Liang et al, 2011;Viaene et al, 2011).…”