Longitudinal study of wind-up responses after graded spinal cord injuries in the adult rat

Purpose: The main objectives of this work were to evaluate the development of neuropathic pain after spinal cord injuries of different severities, and to assess changes in central excitability and plasticity by means of wind-up responses and withdrawal reflexes. Methods: Two groups of rats were subjected to spinal cord contusion with forces of 100 or 200 kdyn applied at T8. Measurements of thermal and mechanical pain thresholds as well as wind-up measurements were performed weekly during two months after injury. Withdrawal reflexes were also assessed electrophysiologically. Results: We found that animals with contusion of different severities showed a similar reduction in nociceptive thresholds. All contused animals showed increased wind-up responses compared to intact animals during the first 2 to 6 weeks post injury. The mean increase of wind-up was higher in rats with stronger spinal cord contusion. Results from the withdrawal reflexes did not correlate with nociceptive behaviors nor wind-up responses, highlighting the plasticity of spinal circuits modulation after SCI. Conclusion: These results indicate that the graded-force spinal cord contusion model is suitable for studying central neuropathic pain, and for assessing changes in wind-up responses. Wind-up measurements can be used as a non-invasive technique to detect changes in central excitability after SCI of different severities.