Figure 9. 5-HT potentiates acid-induced pain-related behavior in mouse via ASIC3 channels. A, Pain-related behavior as determined by the time spent on paw licking following saline or chemical injection (20 μl) as indicated. Means ± SEM. n = 9–14, *p < 0.05, **p < 0.01, and ***p < 0.01, versus as indicated. ##p < 0.01, WT mice versus their KO littermates. Acetic acid, 0.6%, pH 3.5–4.0; 5-HT, 25 μm; amiloride, 200 μm. B, Effects of methysergide (Methy; 40 μm), Y-25130 (200 nm), and AMG9810 (10 μm) on pain behaviors evoked by coapplication of 5-HT (25 μm) and 0.6% acetic acid. n = 8–10. *p < 0.05, compared with coinjection of 5-HT and 0.6% acetic acid. C, Effects of 5-HT (25 μm) on 0.6% acetic acid-induced pain behaviors in ASIC1a KO mice and their WT littermates. Data are means ± SEM n = 8–10. ***p < 0.001 versus as indicated. D, Lack of effect of MK-212 (5-HT2 receptor agonist, 50 μm) and trazodone (Tra; 5-HT2 receptor agonist, 50 μm) on pH 5.0-induced currents in mouse DRG neurons. Ip and Is represent peak current and sustained current, respectively. E, Lack of effect of MK-212 (50 μm) and Tra (50 μm) on potentiating pain behaviors induced by 0.6% acetic acid in ASIC3 KO mice and their WT littermates. *p < 0.05, versus as indicated, indicating the effects of MK-212 or Tra alone. n = 8. F, Lack of effect of BK (50 μm) on pain behaviors induced by 0.6% acetic acid in ASIC3 KO mice and their WT littermates. n = 8–10.