en Nervous system (others) Others Experimental research article Experimental research article Abstract Introduction: Matrix metalloproteinase 2 is one of the inflammatory mediators that is involved in nociceptive processing and its production is regulated by many inflammatory factors such as nitric oxide. We studied the role of MMP-2 on the analgesic effects of nNOS inhibitor. Methods: Considering that nitric oxide has many roles in pain processing, we studied the CSF levels of MMP-2 after hind paw formalin injection (50µl, 2.5%) and neuronal nitric oxide synthase inhibition intrathecally. We also studied the effect of MMP-2 inhibitor on pain behavior and its role on analgesic effect of neuronal nitric oxide synthase (nNOS) inhibitor. Results: Rats that received MMP-2 inhibitor (30mM) showed severe responses to the formalin injection. Pain was reduced after nNOS inhibition. Prior to nNOS inhibitor injection, MMP-2 inhibition reduced the analgesic effects of nNOS inhibitor. Immunological study showed that MMP-2 increased in rats that received nNOS inhibitor. Conclusion: These data suggest the possible roles for MMP-2 in analgesic effect of nNOS inhibitor. matrix metalloproteinase, nitric oxide, formalin test. 10 17 http://ppj.phypha.ir/browse.php?a_code=A-10-192-6&slc_lang=en&sid=1 Fatemeh Khojasteh f_khojasteh@modares.ac.ir 320031947532846005417 320031947532846005417 No Physiology Dept., Tarbiat Modares University Majid Hasanpour-Ezati hassanpm@yahoo.com 320031947532846005418 320031947532846005418 No Biology dept., Shahed University Seyed Javad Mirnajafi-Zadeh mirnajaf@modares.ac.ir 320031947532846005419 320031947532846005419 No Physiology Dept., Tarbiat Modares University Saeed Semnanian ssemnan@modares.ac.ir 320031947532846005420 320031947532846005420 Yes Physiology Dept., Tarbiat Modares University