The effects of botulinum toxin A on mechanical and cold allodynia in a rat model of neuropathic pain

Purpose: Botulinum toxin type A (BoNT-A) has been used to treat many disorders related to excessive muscle contraction, but there are few studies evaluating its effects on neuropathic pain. The aim of this study was to evaluate the analgesic effects of BoNT-A in a rat model of neuropathic pain. Methods: Male Sprague-Dawley rats were prepared by ligating the left L5 and L6 spinal nerves to produce neuropathic pain. Seventy neuropathic rats were randomly assigned into seven groups. Either normal saline or BoNT-A (10, 20, 30 and 40 U(.)kg(-1)) was administered to the plantar surface of the affected left hind paw, and BoNT-A (30 and 40 U(.)kg(-1)) was administered into the unaffected right paw in order to determine the drug-induced systemic effect. Mechanical and cold allodynia were observed at pre-administration, one, three, five, seven and 15 days after drug administration, and were quantified by measuring withdrawal frequencies to stimuli with von Frey filament and 100% acetone, respectively. Rotarod performance was measured to detect drug-induced adverse motor effects. Results: The mean minimum withdrawal frequencies to mechanical and cold stimuli were 77 +/- 11 and 90 +/- 4.5%, 46 +/- 5 and 66 +/- 7%, 33 +/- 7 and 62 +/- 7%, 12 +/- 2.9 and 54 +/- 7.3% with 10, 20, 30 and 40 U(.)kg(-1) BoNT-A respectively (P < 0.05). Doses of 30 and 40 U(.)kg(-1) BoNT-A resulted in reduced rotarod performance time. Conclusion: We conclude that peripherally administered BoNT-A reduces mechanical and cold allodynia in a rat model of neuropathic pain.