Fig. 1

Orexin neuron ablation mice, but not orexin peptide-deficient mice, showed the decrease of pruritogen-induced scratching behavior. A c-Fos expression (green) in orexin neurons (red) in the lateral hypothalamus after intradermal injection of vehicle and chloroquine. B The quantification of c-Fos expression showed a significant increase in c-Fos-positive cells in orexin neurons (%) after the chloroquine treatment compared with the vehicle control. n = 5 for each group. C Time course of the number of scratching behaviors induced by intradermal chloroquine injection. The plots indicate the cumulative number of scratching bouts recorded every 5 min. D The scratching behavior within 30 min after chloroquine injection was significantly decreased in ORX-abl mice (n = 15), but not in ORX-KO mice (n = 7), compared with WT mice (n = 10). WT, wild-type mice; ORX-abl, orexin-neuron-ablated mice; ORX-KO, orexin-peptide-deficient mice. The arrows in A indicate fornix. The white boxed area in A left is magnified in A right. The data represent the mean ± SEM. ***P < 0.001 (unpaired t-test). **P < 0.01 (two-way ANOVA with post hoc Tukey’s multiple comparisons test)