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Fig. 3. The analgesic effects of essential oil of Eucalyptus (EOE) is via the μ-opioid pathway as demonstrated by the formalin test. The relevance of antinociceptive effect of EOE via the opioid pathway was investigated in this experiment. The licking time after pretreatment with an antagonist of the opioid receptor 15 min before the injection of the EOE (45 mg/kg, intraperitoneal) is shown. 5′-guanidinonaltrindole (GNTI, κ-opioid antagonist, 0.3 mg/kg), naltrindole (NTD, δ-opioid antagonist, 5 mg/kg), and naloxone (Nal, μ-opioid antagonist, 4, 8, 12 mg/kg) plus EOE group were injected intraperitoneally. During the second phase, there was a noteworthy variance in licking time between the EOE group and the vehicle group. The naloxone group (8, 12 mg/kg) and the naloxone plus EOE group showed statistically significant differences compared to the EOE treatment group in the second phase. Nal + Mor: naloxone 4 mg/kg + morphine 4 mg/kg. Each value represents the mean and standard error of mean. *P < 0.05, **P < 0.001, compared to the EOE (45 mg/kg) only group. One-way analysis of variance followed by Tuckey’s post hoc test were used to perform the statistical analyses. There were 8 mice in all groups, except there were 7 in the naloxone plus EOE group.
Korean J Pain 2019;32:79~86 https://doi.org/10.3344/kjp.2019.32.2.79
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