Figure 3.
H1R is the main receptor for FGF13-mediated histamine signaling. A, Single-cell RNA sequencing showing the expression profile of histamine receptors, H1R, H2R, H3R, and H4R in the DRG neuron types (C1-C10) of mice. H1R and H2R were primarily expressed in C2 and C4 small DRG neurons, and H3R was mainly expressed in the C3 type of small DRG neurons. H4R was barely expressed in such neurons. B, Whole-cell patch-clamp recording showing AP firing evoked by 1 mm histamine from neurons overexpressing H1R, H2R, H3R, H4R, or vector. Left, Representative AP firing from neurons responding to histamine. The percentage of neurons responding to histamine was the significantly highest when transfected with H1R (n = 6 from 1 or 2 mice each, 36 cells) compared with vector (n = 3 from 1 or 2 mice each, 17 cells), H2R (n = 4 from 1 or 2 mice each, 14 cells), H3R (n = 3 from 1 or 2 mice each, 23 cells), and H4R (n = 4 from 1 or 2 mice each, 19 cells). The patch-clamp recording showed that >60% DRG neurons expressing H2R, H3R, or H4R responded to its agonist, suggesting normal function of these expressed receptors. Data are mean ± SEM. ***p < 0.001 versus vector. C, The behavior test showing reduced scratching number induced by intradermal injection of H1R agonist HTMT within 30 min in Fgf13-/Y mice (n = 7) compared with Fgf13F/Y mice (n = 8). However, the scratching number induced by H2R agonist Dimaprit, H3R agonist immethridine, or H3R antagonist H4R agonist clobenpropit was not significantly changed. Data are mean ± SEM. **p < 0.01 versus Fgf13F/Y mice. D, Whole-cell patch-clamp recording showing that the reduced percentage of neurons responding to histamine in Fgf13-/Y mice (Fgf13F/Y: n = 4 from 3 mice each, 24 cells; Fgf13-/Y: n = 4 from 3 mice each, 17 cells) was rescued by FGF13B overexpression (n = 3 from 2 mice each, 21 cells). Representative AP firing from neurons responding to 1 mm histamine was shown (left). Data are mean ± SEM. **p < 0.01 versus Fgf13F/Y mice. #p < 0.05 versus Fgf13-/Y mice.