en Experimental research article Experimental research article Introduction: In this study the effect of Matricaria recutita extract on acute pain in the presence and absence of flumazenil (antagonist of benzodiazepine) and lesioned paragigantocellularis (PGi) nucleus was investigated. Method: Wistar male rats (250±20 g) were used. Animals were grouped randomly into intact, sham and bilateral lesion of PGi nucleus. Intact and lesioned animals, each divided into 4 subgroups which received saline, M. recutita hydro-alcoholic extract (25 mg/kg), flumazenil (1 mg/kg) and flumazenil + M. recutita. Hot plate test were used for pain thereshold evaluation. Results: Results showed that: In intact animals M. recutita induced analgesic effect but flumazenil had significant hyperalgesic effect. In these animals flumazenil prevented the analgesic effects of M. recutita. Lesion of PGi induced significant hyperalgesia. M. recutita in absence of PGi nucleus showed significant analgesic effect and flumazenil increased pain sensation and caused significant hyperalgesia. The analgesic effect of M. recutita attenuated by flumazenil in absence of PGi nucleus. Conclusion: It seems that PGi nucleus involves in pain modulation but analgesic effect of M. recutita that may be via the benzodiazepine-like activity of some its components does not interact with PGi nucleus. Matricaria recutita, Paragigantocellularis nucleus, Flumazenil, Hot plate. 183 189 http://ppj.phypha.ir/browse.php?a_code=A-10-110-42&slc_lang=en&sid=1 Zahra Abbasi zadeh 320031947532846002947 320031947532846002947 No Mahnaz Kesmati mahnazkessmati@yahoo.com 320031947532846002948 320031947532846002948 Yes Hadi Fathi Moghaddam 320031947532846002949 320031947532846002949 No