Background & objectives: Origanum Vulgare is an herbal plant which is widely distributed in the north and northwest parts of Iran and posses therapeutic properties. The aim of this study was to evaluate the effect of intracerebroventricular (ICV) injection of aqueous extract of Origanum Vulgare L. ssp. viride on pain threshold in male rats.

  Methods: In this study,�28 Male Wistar rats (200-250 g) were divided randomly into 4 groups (n=7) . Rats were anaesthetized with a mixture of ketamine and xylazine and placed in stereotaxic apparatus. A guide cannula was inserted into ventricular area, according to the atlas of Paxinos and Watson. One week after surgery , three groups of rats received microinjection of Origanum extract (1, 3, 6µg/rat). Controls received the microinjection of the same volume of saline. Tail flick latency (TFL) was used to assess the nociceptive response each 15 min for 120 min, using tail flick test. The results were analyzed by repeated measurement test. One-way analysis of variance (ANOVA) was used to compare the mean values of quantitative variable among the groups. The data are expressed as mean ± SEM. p < 0.05 was considered significant.

  Results: Intracerebroventricular administration of the Origanum extract resulted in significant and dose-dependent increase in TFL compared to controls (p<0.05). Origanum extract at dose of 3µg/rat showed the highest analgesic response. The maximum analgesic response was observed at 60 min and 90 min post extract injection (p<0.05).

  Conclusion: These results suggest that the ICV injection of aqueous extract of Origanum Vulgare possesses dose- dependent antinociceptive activities in the tail flick test in rats.