Histamine-induced itchy responses mediated by LHb. a Representative images of Fos expressing LHb after vehicle or histamine injection. Areas surrounded white dotted lines indicate LHb. Brain slices were counterstained with DAPI to identify LHb region. Scale bar, 200 μm. b High magnified images of rectangular region in Fig. 1b. It is noted that, in histamine-injected group, Fos (+) cells were concentrated into the parvocellular (LHbMPc) and central (LHbMC) subnuclei within the medial division of the LHb (LHbM). Scale bar, 200 μm. c Histamine injection tends to increase Fos (+) cells in the overall LHb (n = 9 ~ 10/group; unpaired t-test; t17 = 1.885, p = 0.0767). Veh; Vehicle, His; Histamine. d Histamine-induced Fos expression was significantly increased only in posterior part of LHb (n = 9 ~ 10/group, two-way ANOVA followed by Bonferroni posttest: effect of drug, F(1, 68) = 4.001, p < 0.05; effect of slice, F(3, 68) = 18.35, p < 0.005, effect of interaction, F(3, 68) = 4.232, p < 0.01; posttest, * p < 0.005). e Representative images showing hM4Di-mCherry expression in LHb after the end of behavioral experiments. Areas surrounded white dotted lines indicate LHb. Brain slices were counterstained with DAPI to identify LHb region. Scale bar, 200 μm. f Upper: experimental scheme for testing the role of LHb for itchy information processing. Lower: Histamine-induced scratching responses were inhibited by suppression of LHb activities. (n = 9 ~ 10/ group, one-way ANOVA followed by Tukey’s multiple comparison test; F (2, 26)=22.43, p < 0.001; * P < 0.05, *** p < 0.001)
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