S1-SDH projection neurons have a tonic inhibitory effect on itch behaviors. A Representative image showing the distribution of S1-SDH projection neurons labeled by EGFP without ablation. B Representative image showing the distribution of S1-SDH projection neurons labeled by EGFP after ablation. C Summary of the number of EGFP+ neurons in S1 (n = 3). D, E Effects of ablation of S1-SDH projection neurons on itch behaviors induced by C48/80 (D) or CQ (E) (n = 8). F Effects of ablation of S1-SDH projection neurons on motor function of mice (n = 8). G, H Pharmacogenetic inhibition of S1-SDH projection neurons enhances itch behaviors in response to C48/80 (G, n = 7) or CQ (H, n = 7). I Injection of hM4Di viruses has no effect on the motor function of mice (n = 7). J, K Pharmacogenetic activation of S1-SDH projection neurons reduces itch behaviors in response to C48/80 (J, n = 7) or CQ (K, n = 7). L Injection of hM3Dq viruses has no effect on the motor function of mice (n = 7).