Pain and itch coding mechanisms of polymodal sensory neurons.

Pain and itch coding mechanisms in polymodal sensory neurons remain elusive. MrgprD⁺ neurons represent a major polymodal population and mediate both mechanical pain and nonhistaminergic itch. Here, we show that chemogenetic activation of MrgprD⁺ neurons elicited both pain- and itch-related behavior in a dose-dependent manner, revealing an unanticipated compatibility between pain and itch in polymodal neurons. While VGlut2-dependent glutamate release is required for both pain and itch transmission from MrgprD⁺ neurons, the neuropeptide neuromedin B (NMB) is selectively required for itch signaling. Electrophysiological recordings further demonstrated that glutamate synergizes with NMB to excite NMB-sensitive postsynaptic neurons. Ablation of these spinal neurons selectively abolished itch signals from MrgprD⁺ neurons, without affecting pain signals, suggesting a dedicated itch-processing central circuit. These findings reveal distinct neurotransmitters and neural circuit requirements for pain and itch signaling from MrgprD⁺ polymodal sensory neurons, providing new insights on coding and processing of pain and itch. [Display omitted] • Polymodal MrgprD⁺ primary afferent neurons express Vglut2 and Nmb • Glutamate is required for both pain and itch signaling from MrgprD⁺ neurons • NMB is selectively required for itch signaling • NMBR⁺ central neurons are required for MrgprD⁺-neuron-mediated itch signals Guo et al. identify the pain and itch coding mechanisms of MrgprD⁺ primary afferent neurons. While only glutamate is required for mechanical pain signals mediated by this population, the neuropeptide neuromedin B (NMB) and a subthreshold quantity of glutamate are released together to excite NMB-sensitive postsynaptic circuits for itch signals. [ABSTRACT FROM AUTHOR]