Recently, we have demonstrated distinct roles of MMP-9 and MMP-2 in neuropathic pain development: (i) transient MMP-9 up-regulation after nerve injury is critical for the early-phase development of neuropathic pain; (ii) sustained MMP-2 up-regulation maintains neuropathic pain; and (iii) MMP-9 and MMP-2 induce the active cleavage of IL-1β (activation) in early and late-phase of nerve injury, respectively [28,30]. This evidence concerns the gene MMP9 and neuropathic pain.