Transcriptomic and spatial organization of mouse spinal cord projection neurons.

The spinal cord projection neurons (SPNs) convey diverse modalities of somatosensory information from the spinal cord to the brain, but their molecular and cellular heterogeneity and organization remain largely unknown. Using retrograde labeling and single-cell transcriptomic analysis, we identified 15 SPN subtypes in the mouse cervical spinal cord, including a group of previously unknown GABAergic SPN subtypes, and we found distinct lamina preferences in soma distribution. Brain-wide mapping of SPN projections revealed distinct subtype-dependent projection patterns. The existence of GABAergic SPNs was further demonstrated by single-neuron projectome analysis and electrophysiological recording of inhibitory spinal inputs at target brain areas. Using gene set-based classification, we identified coherent expression of functional gene modules across SPN subtypes, supporting their transcriptional distinction and functional specialization. Finally, distinct SPN subtypes were shown to be differentially involved in pain and itch processing. These results provide a framework for deciphering molecular and cellular mechanisms underlying somatosensory processing.