pISSN 1226-4512 eISSN 2093-3827

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Original Article

Korean J Physiol Pharmacol 2008; 12(6): 299-306

Published online December 30, 2008 https://doi.org/10.4196/kjpp.2008.12.6.299

Copyright © Korean J Physiol Pharmacol.

Long-term Follow-up of Cutaneous Hypersensitivity in Rats with a Spinal Cord Contusion

Ji-In Jung1, Junesun Kim2, Seung Kil Hong1, and Young Wook Yoon1

1Department of Physiology and Neuroscience Research Center, Korea University College of Medicine, 2Department of Physical Therapy, Korea University College of Health Science, Seoul 136-705, Korea

Abstract

Sometimes, spinal cord injury (SCI) results in various chronic neuropathic pain syndromes that occur diffusely below the level of the injury. It has been reported that behavioral signs of neuropathic pain are expressed in the animal models of contusive SCI. However, the observation period is relatively short considering the natural course of pain in human SCI patients. Therefore, this study was undertaken to examine the time course of mechanical and cold allodynia in the hindpaw after a spinal cord contusion in rats for a long period of time (30 weeks). The hindpaw withdrawal threshold to mechanical stimulation was applied to the plantar surface of the hindpaw, and the withdrawal frequency to the application of acetone was measured before and after a spinal contusion. The spinal cord contusion was produced by dropping a 10 g weight from a 6.25 and 12.5 mm height using a NYU impactor. After the injury, rats showed a decreased withdrawal threshold to von Frey stimulation, indicating the development of mechanical allodynia which persisted for 30 weeks. The withdrawal threshold between the two experimental groups was similar. The response frequencies to acetone increased after the SCI, but they were developed slowly. Cold allodynia persisted for 30 weeks in 12.5 mm group. The sham animals did not show any significant behavioral changes. These results provide behavioral evidence to indicate that the below-level pain was well developed and maintained in the contusion model for a long time, suggesting a model suitable for pain research, especially in the late stage of SCI or for long term effects of analgesic intervention.

Keywords: Central neuropathic pain, Spinal cord injury, Mechanical allodynia, Spinal cord contusion, Cold allodynia