ABSTRACT
<p><b>OBJECTIVE</b>To investigate the effects of intrathecal ouabain and tizanidine injection for treatment of neuropathic pain in rats.</p><p><b>METHODS</b>Male SD rats weighing 250-300 g were randomly divided into 5 groups (n = 6), namely the control group, ouabain group, tizanidine group, combined ouabain and tizanidine injection group, and the antagonist group. Intrathecal catheter was implanted 7 days before spinal nerve ligation to establish the neuropathic pain model. Mechanical withdrawal threshold (MWT) before and after intrathecal administration of the agents was recorded in the rats. Isobolographic analysis was performed to evaluate the interactions between the agents.</p><p><b>RESULTS</b>Intrathecal injection of ouabain (0.25-5 microg) or tizanidine (0.5-5 microg) alone produced dose-dependent analgesic effect against the neuropathic pain (P < 0.05). Isobolographic analysis revealed a synergistic interaction between ouabain and tizanidine. Intrathecal pretreatment with atropine (5 microg) or yohimbine (20 microg) antagonized the effects of ouabain and tizanidine administered alone or in combination (P < 0.05).</p><p><b>CONCLUSION</b>Intathecal injection of ouabain or tizanidine produces dose-dependent analgesic effects against neuropathic pain, and their synergistic effect after combined injection probably involves the cholinergic transmission and alpha2 receptor.</p>