Investigation of the Antinociceptive Activity of the Hydroethanolic Extract of Junglas nigra Leaf by the Tail-Immersion and Formalin Pain Tests in Rats.

Background: Juglans (J.) nigra leaf is obtained from a plant that is used in traditional medicine in some countries to alleviate inflammatory diseases. Aim: The aim of this study was to compare the effects of J. nigra extract on acute nociceptive and inflammatory pain in rats. Methods: Antinociceptive activity was examined in Wistar rats by the tail-immersion and formalin tests. Motor function was assessed using the rotarod test. Plant extract was administered intraperitoneally. Results: In the tail-immersion test, the maximal antinociceptive effect of the plant extract (100-330 mg/kg) was about 24-30% and is the result of the effect of a high concentration of ethanol. In the formalin test, the plant extract (41.3-330 mg/kg) significantly and dose-dependently inhibited nociception in both phases of the test with similar maximal effects of about 76% and 85%. Only the plant extract at the dose of 330 mg/kg caused a significant time-dependent reduction in time spent on the rotarod. Conclusions: In rats, the preventive systemic administration of the hydroethanolic extract of J. nigra leaf reduced chemically but not thermally induced pain. Higher efficacy was obtained in pain associated with inflammation and tissue injury. The antinociceptive effect is dose-dependent and may be limited by motor impairment.