Neuronal atlas of the dorsal horn defines its architecture and links sensory input to transcriptional cell types

Abstract

The dorsal horn of the spinal cord is critical to processing distinct modalities of noxious and innocuous sensation, but little is known of the neuronal subtypes involved, hampering efforts to deduce principles governing somatic sensation. Here we used single-cell RNA sequencing to classify sensory neurons in the mouse dorsal horn. We identified 15 inhibitory and 15 excitatory molecular subtypes of neurons, equaling the complexity in cerebral cortex. Validating our classification scheme in vivo and matching cell types to anatomy of the dorsal horn by spatial transcriptomics reveals laminar enrichment for each of the cell types. Neuron types, when combined, define a multilayered organization with like neurons layered together. Employing our scheme, we find that heat and cold stimuli activate discrete sets of both excitatory and inhibitory neuron types. This work provides a systematic and comprehensive molecular classification of spinal cord sensory neurons, enabling functional interrogation of sensory processing.

Expression of cholecystokinin by neurons in mouse spinal dorsal horn

“…The CCK cells represent a large subset of excitatory interneurons, accounting for around a third of those in deeper laminae, and it is therefore not surprising that ablation results in a dramatic behavioral phenotype. Our findings, together with those of Häring et al (), suggest that CCK cells include functionally distinct subsets, such as those that co‐express PKCγ. The extensive overlap between CCK and PKCγ that we observed, taken together with earlier studies that have implicated PKCγ cells in neuropathic pain, raise the possibility that the CCK+/PKCγ+ cells may be particularly important for the development of mechanical allodynia.…”

“…A recent transcriptomic study by Häring et al (2018) identified 15 classes of excitatory dorsal horn neuron, and their results are broadly consistent with the findings described above, as their classes include cells with high levels of the mRNAs for neurotensin, NKB, and substance P. Another peptide that featured in their classification scheme was cholecystokinin (CCK), which was expressed in three separate populations of excitatory neurons. Early reports had indicated that neurons with CCK mRNA were most numerous in lamina III and scattered through the other laminae (Abelson & Micevych, 1991;Cortes, Arvidsson, Schalling, Ceccatelli, & Hokfelt, 1990;Schiffmann, Teugels, Halleux, Menu, & Vanderhaeghen, 1991), while a recent study found that CCK defined a specific population of excitatory neurons in the deeper laminae of the dorsal horn (Abraira et al, 2017).…”

“…Häring et al () used clustering of transcriptomic data to define 15 populations of excitatory neuron, which they named Glut1‐15. Their analysis generally supports our earlier findings, by showing that mRNAs for substance P, neurotensin, and NKB are highly expressed by different populations: Glut10‐11 for substance P, Glut4 for neurotensin, and Glut5‐6 for NKB.…”

“…Sections were scanned with a Zeiss LSM 710 confocal microscope through the 40× oil-immersion lens with the confocal aperture set to 1 Airy unit. In each case, a single optical plane through the middle of the section was scanned (Häring et al, 2018)…”

Emerging links between cerebrovascular and neurodegenerative diseases—a special role for pericytes

“…Thus, more than 500 molecularly distinct classes of neurons and glial cells have been identified in the mouse brain [1,2], and information about the cellular composition of specific brain regions is increasing rapidly [2][3][4][5][6][7][8]. In addition, there is an even larger number of supporting glial cells, i.e., astrocytes and oligodendrocytes, the latter forming myelin sheets around neurons and making up a large part of the white matter in the brain.…”