Opioid receptors role on anti-nociceptive effects of the aqueous extracts of Melissa Officinalis in mice

Introduction: Melissa Officinalis (MO) overgrows in different parts of Iran. In previous studies, ethanol extract of aerial parts (leaf & stem) of MO showed anti-nconvulsant and sedative effects in rats. This study was designed to evaluate anti-nociceptive effects in different doses of aqueous decoction extracts of MO and the role of opioid receptors in rats. Methods: In this experimental study, 63 male mice (weighing 25-30g) in Tail Flick model were examined. Different doses of extract (5, 10, 25, 50 mg/kg IP-MO) were injected to the separate groups and saline (10ml/kg-IP) was injected intrapeditoneal in control group. In four groups the role of opioid receptors (Naloxone 2mg.kg) was designed to evaluate anti-nociceptive effects in the aqueous decoction extracts of MO (5mg/kg) and 25 minutes after the injection the anti-nociceptive effect was evaluated. Analysis of variance was used to analysis the data. Results: The results showed that average time of Tail Flick had significant difference in two groups (P<0.0001) but the test groups had no significant difference in different doses. Based on the results, naloxone caused reduction in antinociceptive effects of 5 mg/kg Melissa Officinalis dose (P<0.0001). Conclusion: It is concluded that the aqueous extract of MO has anti-nociceptive activity which is not dose related, and is probably related to opioid receptors. Determination of other receptors which may have anti-nociceptive activity needs further investigation.