Evaluation of antinociceptive effect of Aegiceras corniculatum stems extracts and its possible mechanism of action in rodents

Ethnopharmacological relevance: Aegiceras corniculatum (Linn.) Blanco is used in various traditional medicinal system(s) for the treatment of rheumatism, painful arthritis and inflammation. Therefore, the pharmacological studies of its antinociceptive effect was undertaken to validate its traditional use. Materials and methods: n-Hexane, ethyl acetate and methanol extract(s) derived from Aegiceras corniculatum (stems) were studied using various nociceptive model(s) induced chemically or thermally in mice including acetic acid-induced writhing, formalin-induced paw licking and hot plate test. Results: In acetic acid-induced writhing test, plant extracts dose dependently decreased the writhing numbers. The methanolic extract (1-10 mg/kg, i.p. in mice) of the plant was more potent than acetaminophen and acetyl salicylic acid, with an IC50 of 4.2 +/- 0.99 mg/kg. Moreover, the time of nociceptive behaviors induced by intraplantar formalin injection was also suppressed during 1st and 2nd phases in the presence of ethyl acetate extract whereas, n-hexane and methanolic extracts inhibited the paw licking in mice during the 1st (IC50 12 +/- 0.76 mg/kg) and 2nd phases (IC50 3.8 +/- 0.55 mg/kg). Naloxone, beta-funaltrexamine, and naltrindole antagonized the n-hexane extract-induced antinociception in the first phase of formalin test indicating its non-selective analgesic response via opioid receptor(s). However, ethyl acetate extract was devoid of any opioid action. Additionally, these extracts significantly inhibited the pain stimulation in hot plate test. Withdrawal syndrome of morphine dependence was also diminished in the presence of plant extracts via potentiation of GABAergic system. Conclusion: These results suggested that Aegiceras corniculatum extract(s) possesses analgesic properties and acts on the central nervous system, thereby suppressing the inflammatory pain justifying its folklore use. (C) 2011 Elsevier Ireland Ltd. All rights reserved.