Fig. 5: GRP⁺ interneurons and GRP are required for morphine-induced itch.

A In situ hybridization RNAscope images of Npy1r (White) and Grp (red) mRNA in mouse SDH of WT mice, yellow arrows indicate Npy1r double labeled with Grp, Scale bar = 10 μm. B The percentage of co-expression between Npy1r⁺ and Grp⁺ neurons in SDH, 14 spinal cord sections from 6 mice were analyzed. C Morphine-induced itch was significantly inhibited in Grp^Cre;iDTR mice, Diphtheria toxin (50 μg/kg, 5 μg/mL in sterile PBS) was intraperitoneal injected every other day, one week before intrathecal injected morphine (0.3 nmol), student’s unpaired two-tailed t-test. D Morphine (0.3 nmol)-induced itch was significantly inhibited by chemogenetic inhibition Grp⁺ neurons in Grp^Cre;hM4Di mice following CNO injection (10 nmol), student’s unpaired two-tailed t-test. E Morphine (0.3 nmol)-induced itch was significantly inhibited in Vglut2^Cre;Grp^fl/fl mice. Student’s unpaired two-tailed t-test. F Intrathecal morphine (0.3 nmol)-induced itch was inhibited by co-injection of GRPR antagonist PD176252 (10 μg) in WT mice, student’s unpaired two-tailed t-test. Data are shown as means ± SEM. P values are indicated in the figures. Sample sizes are presented in parentheses. Source data are provided as a Source Data file. Created in BioRender. Wang, Z. (2025) https://BioRender.com/oklxfey.