A New Animal Model Of Brachial Plexus Neuralgia Produced By Injrction Of Cobra Venom Into The Lower Trunk In The Rat

Objective: To establish a new animal model for the study of neuropathic pain developed by administration of cobra venom to the brachial plexus lower trunk.Methods: Fifty-eight adult male Sprague-Dawley rats were randomly divided into 5 groups:(1) control group(n=10);(2) sham-operated group(n=12);(3) cobra venom group(n=12);(4) pregabalin test postoperative day(POD) 1(n=12) and pregabalin test postoperative day12(n=12).Under pentobarbital sodium anesthesia,an incision was made 1cm in length, running from the sternum to the axillary region in the supine position. The lower trunk of brachial plexus, with subclavian vessel,were located under the pectoralis major muscle group. Cobra venom was injected into the lower trunk. In the sham-operated group, saline was injected into the lower trunk by using the same procedure. The control group was not given any intervention.On postoperative day 1 and day12, pregabalin was administered intragastricly at30mg/kg in two groups. The drug treatment repeatedly delivered 6 days. Mechanical withdrawal thresholds(MWT) were tested with von Frey filaments in the right hindpaw and the left forepaw and video recordings were used to analyze the spontaneous behaviors at 3d before the operation and 3, 6, 9, 12, 15, 20, 30, and 60 days after the operation. Two rats were taken from the sham-operated group, cobra venom group and pregabalin test POD1 and 12 groups, respectively to for electron microscope examination on day 14 and 60 day after surgery. The brachial plexus(BP)and cervical cord(C8-T1) were observed after the mice were perfused intracardially.Results: In comparison to the blank and sham-operated group, cobra venom-treated rats showed a profound decrease in the MWT, exploratory and increased grooming behaviors(P <0.05). The changes were long-lasting(up to 60days), in both ipsilateral and contralateral paws. Furthermore, it was observed under microscopic examination that the myelin sheath was demyelinated in the BP and cervical cord(C8-T1) after injection of cobra venom to the lower trunk. Pregabalingroup rats showed changes in MWT and spontaneous behaviors after pregabalin treatment at post-operative day 1(P<0.05), and returned to the level of control group at 6 days after operation compared with the control and sham-operated groups(P>0.05). In pregabalin test POD12 group, the decreased MWT and the increased grooming behavior were improved at 20 days after operation(P>0.05). However,pregabalin had no effect on exploratory activity(P<0.05). Results indicate that pregabalin effectively attenuates mechanical hyperalgesia in acute period.Conclusions:1 Administration of snake venom into the brachial plexus lower trunk of the rat could produce allodynia, successfully to establish an animal model of brachial plexus neuralgia.2 The brachial plexus and cervical cord underwent demyelination alterations after injection of cobra venom to the lower trunk.3 Pregabalin effectively attenuates mechanical hyperalgesia in acute period.