SUMMARY Primary afferents are known to be inhibited by kappa opioid receptor (KOR) signaling. However, the specific types of somatosensory neurons that express KOR remain unclear. Here, using a newly developed KOR-cre knockin allele, viral tracing, single-cell RT-PCR, and ex vivo recordings, we show that KOR is expressed in several populations of primary afferents: a subset of peptidergic sensory neurons, as well as low-threshold mechanoreceptors that form lanceolate or circumferential endings around hair follicles. We find that KOR acts centrally to inhibit excitatory neurotransmission from KOR-cre afferents in laminae I and III, and this effect is likely due to KOR-mediated inhibition of Ca2+ influx, which we observed in sensory neurons from both mouse and human. In the periphery, KOR signaling inhibits neurogenic inflammation, nociceptor sensitization by inflammatory mediators, and pain and itch behaviors. These experiments provide a rationale for the therapeutic use of peripherally restricted KOR agonists.

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All authors have no conflict of interest. Acknowledgements:The authors acknowledge and thank Mr. Christopher Sullivan for expert technical support and mouse husbandry.Author contributions: KAM, conception and design, acquisition of data, analysis and interpretation of data, drafting and revising the article. PCA and RLF, acquisition of data, analysis and interpretation of data. KMA, HRK and BMD, conception and design, analysis and interpretation of data, drafting and revising the article.