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The Master Switch for Itch?
Recently, gastrin-releasing peptide (GRP) has been implicated as the primary neurotransmitter between itch-sensitive nerve fibers and downstream neurons in the spinal cord. However, Mishra and Hoon (p. 968) challenge this view, provide evidence that natriuretic polypeptide b (Nppb) is the central itch neurotransmitter, and suggest that GRP is released by second-order neurons in the spinal dorsal horn that express the Nppb receptor and are excited by Nppb.
Abstract
Itch is triggered by somatosensory neurons expressing the ion channel TRPV1 (transient receptor potential cation channel subfamily V member 1), but the mechanisms underlying this nociceptive response remain poorly understood. Here, we show that the neuropeptide natriuretic polypeptide b (Nppb) is expressed in a subset of TRPV1 neurons and found that Nppb−/− mice selectively lose almost all behavioral responses to itch-inducing agents. Nppb triggered potent scratching when injected intrathecally in wild-type and Nppb−/− mice, showing that this neuropeptide evokes itch when released from somatosensory neurons. Itch responses were blocked by toxin-mediated ablation of Nppb-receptor–expressing cells, but a second neuropeptide, gastrin-releasing peptide, still induced strong responses in the toxin-treated animals. Thus, our results define the primary pruriceptive neurons, characterize Nppb as an itch-selective neuropeptide, and reveal the next two stages of this dedicated neuronal pathway.
