Abstract
Whisker detection is crucial to adapt to the environment for some animals, but how the nervous system processes and integrates whisker information is still an open question. It is well-known that two main parallel pathways through Ventral posteromedial thalamic nucleus (VPM) ascend to the barrel cortex, and classical theory suggests that the cross-talk from trigeminal nucleus interpolaris (Sp5i) to principal nucleus (Pr5) between the main parallel pathways contributes to the multi-whisker integration in barrel columns. Moreover, some studies suggest there are other cross-streams between the parallel pathways. To confirm their existence, in this study we used a dual-viral labeling strategy and high-resolution, large-volume light imaging to get the complete morphology of individual VPM neurons and trace their projections. We found some new thalamocortical projections from the ventral lateral part of VPM (VPMvl) to barrel columns. In addition, the retrograde-viral labeling and imaging results showed there were the large trigeminothalamic projections from Sp5i to the dorsomedial section of VPM (VPMdm). Our results reveal new cross-streams between the parallel pathways through VPM, which may involve the execution of multi-whisker integration in barrel columns.
Highlights
How the brain builds up a representation of the surrounding world is crucial in neuroscience (Diamond et al, 2008), and the study of sensory systems helps reveal the mechanism by which the nervous system processes and responds to specific sensory input (Feldmeyer et al, 2013)
We found that VPMvlcross neurons and VPMc neurons have no statistical difference in the soma volume, the length, and the total number of branches of dendrites and axons in barrel columns, S1BF, reticular nuclei (Rt), and in the whole cortex (Figures 5B–G and Supplementary Figures S4A–E)
We identified the new anatomical cross-streams in ventral posterior medial nucleus (VPM), including the outputs of VPMvl neurons projecting to barrel columns, and the inputs of VPMdm received from Sp5i (Figure 8)
Summary
How the brain builds up a representation of the surrounding world is crucial in neuroscience (Diamond et al, 2008), and the study of sensory systems helps reveal the mechanism by which the nervous system processes and responds to specific sensory input (Feldmeyer et al, 2013). There is a cross-talk that happens from Sp5i to principal nucleus Pr5 in the brainstem between the parallel streams (Timofeeva et al, 2004; Kwegyir-Afful et al, 2005). This cross-talk endues typical parallel streams through VPM, the structural basis to multi-whisker integration of barrel columns (Kwegyir-Afful et al, 2005). The current research shows that the circuit foundation for multi-whisker integration is very complicated and needs to be further revealed
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