Fig. 3

Early administration of histidine is crucial for its analgesic effect. Histidine given intraperitoneally once daily through 0–3 days PO or 0–1 day PO alleviated mechanical allodynia (a, c) and thermal hyperalgesia (b, d) following PSL during the period of treatment, whereas it had no effect if administered through 4–7 days PO or 2–3 days PO. *P < 0.05, **P < 0.01, compared with the vehicle-treated group. ^## P < 0.01, compared with the baseline. n = 7–9/group