Subset of cortical layer 6b neurons selectively innervates higher order thalamic nuclei in mice

Anna Hoerder-Suabedissen, Shuichi Hayashi, Louise Upton, Zachary Nolan, Diana Casas-Torremocha, Eleanor Grant, Sarada Viswanathan, Patrick O. Kanold, Francisco Clasca, Yongsoo Kim, Zoltán Molnár

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34 Scopus citations

Abstract

The thalamus receives input from 3 distinct cortical layers, but input from only 2 of these has been well characterized. We therefore investigated whether the third input, derived from layer 6b, is more similar to the projections from layer 6a or layer 5. We studied the projections of a restricted population of deep layer 6 cells (“layer 6b cells”) taking advantage of the transgenic mouse Tg(Drd1a-cre)FK164Gsat/Mmucd (Drd1a-Cre), that selectively expresses Cre-recombinase in a subpopulation of layer 6b neurons across the entire cortical mantle. At P8, 18% of layer 6b neurons are labeled with Drd1a-Cre::tdTomato in somatosensory cortex (SS), and some co-express known layer 6b markers. Using Cre-dependent viral tracing, we identified topographical projections to higher order thalamic nuclei. VGluT1+ synapses formed by labeled layer 6b projections were found in posterior thalamic nucleus (Po) but not in the (pre)thalamic reticular nucleus (TRN). The lack of TRN collaterals was confirmed with single-cell tracing from SS. Transmission electron microscopy comparison of terminal varicosities from layer 5 and layer 6b axons in Po showed that L6b varicosities are markedly smaller and simpler than the majority from L5. Our results suggest that L6b projections to the thalamus are distinct from both L5 and L6a projections.

Original languageEnglish (US)
Pages (from-to)1882-1897
Number of pages16
JournalCerebral Cortex
Volume28
Issue number5
DOIs
StatePublished - 2018

All Science Journal Classification (ASJC) codes

  • Cognitive Neuroscience
  • Cellular and Molecular Neuroscience

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    Hoerder-Suabedissen, A., Hayashi, S., Upton, L., Nolan, Z., Casas-Torremocha, D., Grant, E., Viswanathan, S., Kanold, P. O., Clasca, F., Kim, Y., & Molnár, Z. (2018). Subset of cortical layer 6b neurons selectively innervates higher order thalamic nuclei in mice. Cerebral Cortex, 28(5), 1882-1897. https://doi.org/10.1093/cercor/bhy036