This study investigated the antinociceptive effects of aqueous extract of Murraya koenigii (AEMK) leaves (200, 400 and 800 mg/kg, orally) on animal models of acute and persistent pain and its modulation by naloxone.Antinociceptive effects were assessed using tail-flick, hot plate and formalin tests in mice. To differentiate between central and peripheral antinociceptive effect of AEMK, naloxone (2 mg/kg) was administered along with the 800 mg/kg dose of extract. Morphine was used as a standard drug.AEMK and morphine significantly increased the tail-flick latency (tfl) and paw licking/jumping latency in tail-flick and hot plate tests, respectively, in comparison to control. Also, in both the tests AEMK and morphine significantly increased the AUC0-120 min. In formalin test, AEMK (400 mg/kg and 800 mg/kg) and morphine significantly reduced licking time in both early and late phases in comparison to control.Thus, in all three pain models AEMK showed antinociceptive effect, which was blocked by naloxone suggesting the involvement of opioidergic central mechanism.
