Antinociceptive effects of hydroalcoholic extract of Thymus vulgaris.

Previous investigation has shown that Thymus Vulgaris (TV) modulates pain. The aim of this work was to examine the role of TV on acute and chronic pain and compares its effect with dexamethasone (DEX) and stress (ST) by using hot plate, tail flick and formalin tests in mice. In this study male albino mice (25-30 g.) in 21 groups (n=147) were used. TV (100, 500 and 1000 mg/kg), DEX (0.5, 1 and 2 mg/kg) and vehicle (VEH) were injected 30 minutes before pain assessment tests. Stress was applied by 1 min swimming in cold water (18-22 degrees ). Acute and chronic pain was assessed by hot plate, tail flick and formalin tests. For assessment of the role of opioid receptors in antinoceception of TV extract, Naloxon (NAL, 2mg/kg, ip) as opioid receptor antagonist was injected before the injection of the more effective dose (500 mg/kg) of TV extract. Results indicated that TV, DEX and ST have analgesic effects in all tests (P<0.01 in comparison with control group). Above findings showed that TV extract, DEX and ST have modulatory effects on acute and chronic pain. Further research is required to determine the mechanisms by which TV extract has an inhibitory effect on pain sensation.