Effect of immunosuppressant to neuropathic pain

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Using the chronic constriction model of Bennett and Xie (Pain 33, 1988), we investigated whether cyclosporine attenuates mechanical allodynia and hypersensitivity of rats for 70 days after surgery. In addition, we compared cyclosporine to betamethasone, which has potent anti-inflammatory effect, in treating neuropathic pain state.Thirty rats of 62, which showed tactile allodynia measured with von Frey hair at 2nd day after surgery, was randomly allocated to 6 groups (n=5 in each groups). Four groups received cyclosporine (0.01, 0.1, 1 and 10 mg/kg) intraperitoneally. The fifth group received betamethasone sodium phosphate 1 mg/kg, and the sixth group received equal volume of saline. Those injections were started on 2 days after sciatic nerve constriction and given daily for 20 days. Tactile allodynia, mechanical hyperalgesia and heat hyperalgesia were assessed for 70 days.Tactile allodynia was observed on both ipsi- and contralateral side of nerve constriction in all groups. Contralateral heat hyperalgesia was observed in saline and 0.01 mg/kg of cyclosporine injected groups. Similar contralateral mechanical hypersensitivity was not seen. Cyclosporine alleviated tactile allodynia, heat hypersensitivity and mechanical hypersensitivity in dose response manner, although betamethasone showed less potent effect. Body weight gain was less in betamethasone received rats than other groups on the last treatment day.These results indicate possible effects of cyclosporine to treat neuropathic pain. The treatment with cyclosporine seems to be effective even if it was started after nerve injury.