• Mi Geum Lee, Billy K Huh, Sang Sik Choi, Dong Kyu Lee, Byung Gun Lim, and Mikyoung Lee.
• Department of Anesthesiology and Pain Medicine, Gachon University Dongincheon Gil Hospital, Incheon, Korea.
• Pain Physician. 2012 Jul 1;15(4):287-96.

BackgroundResiniferatoxin (RTX) is a potent synthetic agonist for transient receptor potential vanilloid subtype 1 (TRPV1), which has a selectivity for antinociception. The analgesic effect of epidural RTX in a rat model of neuropathic pain has not yet been studied.ObjectivesThe purpose of this study was to evaluate the analgesic effect of epidural RTX on neuropathic pain in a rat model to mechanical and thermal stimulation. The dose-related behavior changes and side effects were also studied.Study DesignA randomized, experimental trial.SettingDepartment of Anesthesiology and Pain Medicine, Korea University Guro HospitalMethodsA spinal nerve ligation model was prepared using male Sprague-Dawley rats (7 weeks old, weight 230-250 g). An epidural catheter was placed at the L4-L5 level. Each study group (n = 6) received a different dose of RTX: 100 ng, 500 ng, 1 μg, 2 μg, 4 μg and 10 μg. All substances were administered in 20 μL volume doses. The control group (n = 6) received 20 μL of normal saline. We evaluated the response to mechanical and thermal stimuli as well as the sedation score at both short-term (3 hours) and long-term (20 days) after the epidural RTX injection.ResultsProlonged analgesia to thermal stimulation was preceded by a transient dose-dependent hyperalgesia (500 ng, 1 μg) or sedation (>/= 2 μg) during the initial 60 minutes after RTX administration. Marked sedation and hyperventilation were noted at higher doses (>/= 2 μg), while 2 out of 6 rats died with a 10 μg dose. ED50 for epidural RTX was 265 ng (95% confidence interval 216.1-324.9 ng). The increased latency to thermal stimulation continued for 20 days at RTX >/=1 μg. But the threshold to mechanical stimulation increased only in the acute period and returned to the baseline after 3-5 days, regardless of the administered dose.LimitationsA histological examination by electron-microscopic staining was not performed. The observation period was not very long (20 days).ConclusionRTX has potential to be used in an epidural route for neuropathic pain in a rat model with a relatively small amount, which produces transitory improvement of mechanical hypersensitivity and prolonged thermal analgesic response.

18 keywords...

hide…