Fig. 5
Blocking histamine synthesis or histamine H1 receptors abolished the analgesic effects of histidine. Histidine (200 mg/kg, i.p.) administered once daily through 0–7 days PO alleviated hypersensitivity in wild-type mice, but not in HDC−/− mice (a, b). Histidine (100 mg/kg, i.p.) did not show any analgesic effect if α-FMH (50 μg, i.c.v) was administered simultaneously (c, d). Mepyramine (200 ng/rat, i.t. or i.c.) but not cimetidine (200, 500 ng/rat, i.t. or i.c.) abolished the analgesic effect of histidine (e–h). *P < 0.05, **P < 0.01, compared with the vehicle-treated group. ## P < 0.01, compared with the baseline. $ P < 0.05, compared with the indicated groups. n = 7–9/group