Comparison of Mechanical Allodynia and Recovery of Locomotion and Bladder Function by Different Parameters of Low Thoracic Spinal Contusion Injury in Rats.

Background: The present study was designed to examine the functional recovery following spinal cord injury (SCI) by adjusting the parameters of impact force and dwell-time using the Infinite Horizon (IH) impactor device. Methods: Sprague-Dawley rats (225−240 g) were divided into eight injury groups based on force of injury (Kdyn) and dwell time (seconds), indicated as Force-Dwell time: 150-4, 150-3, 150-2, 150-1, 150-0, 200-0, 90-2 and sham controls, respectively. Results: After T10 SCI, higher injury force produced greater spinal cord displacement (P ＜ 0.05) and showed a significant correlation (r = 0.813) between the displacement and the force (P ＜ 0.05). In neuropathic pain-like behavior, the percent of paw withdrawals scores in the hindpaw for the 150-4, 150-3, 150-2, 150-1 and the 200-0 injury groups were significantly lowered compared with sham controls (P ＜ 0.05). The recovery of locomotion had a significant within-subjects effect of time (P ＜ 0.05) and the 150-0 group had increased recovery compared to other groups (P ＜ 0.05). In addition, the 200-0 and the 90-2 recovered significantly better than all the 150 kdyn impact groups that included a dwell-time (P ＜ 0.05). In recovery of spontaneous bladder function, the 150-4 injury group took significantly longer recovery time whereas the 150-0 and the 90-2 groups had the shortest recovery times. Conclusions: The present study demonstrates SCI parameters optimize development of mechanical allodynia and other pathological outcomes. (Korean J Pain 2016; 29: 86-95)