Fig. 4.

Effect of naloxone (A), methysergide (B) and yohimbine (C) injected intraperitoneally (i.p.) on inhibition of the writhing response induced by hop extract administered orally. Naloxone (5 mg/kg), Methysergide (5 mg/kg) or yohimbine (5 mg/kg) was pretreated intraperitoneally for 10 min, before oral administration of vehicle or hop extract (100 mg/kg). Hop extract or vehicle was administered orally and then, 0.25 ml of 1% acetic acid solution was injected i.p. 30 min after treatment. The number of writhing was counted for 30 min following acetic acid injection. The vertical bars denote the standard error of the mean. The number of animal used for each group was 8~10 (^***p<0.001, compared with control group).