Central analgesic activity of Litsea polyantha Juss. bark extract

The sensation of pain is initiated in peripheral pain receptors (nociceptors) and its purpose is to draw attention to tissue damage. In order to test analgesic activity, it is obviously necessary to induce pain in the subject and then modify the response to, or perception of, this pain. Analgesic studies of the methanol (90% v/v) extract (MELP) of Litsea polyantha Juss. bark (Yield: 11.79% w/w) was carried out using healthy adult Swiss albino mice of either sex weighing between 20 to 25 g respectively. The experiment protocols were approved by the Institutional Animal Ethical Committee (621/02/ac/CPCSEA) prior to the conduct of the animal experiments. The animals were divided into 6 groups (n=6). Group I and II were used as control, received 10% v/v propylene glycol (PG) and distilled water (DW) at the dose of 10 ml/kg b.w. Group III, IV & V were treated with MELP (50, 75 and 100 mg/kg b.w., i.p.), respectively; Group VI received Morphine sulphate (10 mg/kg b.w., s.c.) an opioid analgesic as standard drug. A reduction in the tail withdrawal as compared to the control group was considered as evidence for the presence of analgesia. Tail flick latency was measured 30 min after the drug administration and Pain Inhibition Percentage (PIP) was calculated. MELP given by intraperitoneal route in mice showed significant and dose-dependent central analgesic activity (P<0.001) at all dose levels. MELP showed 22.2% – 60.4% increase in PIP in tail flick test and 21.2% – 67.8% increase in PIP in tail immersion method.