At-level allodynia after mid-thoracic contusion in the rat

Abstract

The rat mid-thoracic contusion model has been used to study at-level tactile allodynia after spinal cord injury (SCI), one of the more common types of allodynia. An important advantage of this model is that not all animals develop allodynia and, therefore, it could be used to more clearly examine mechanisms that are strictly related to pain development separately from mechanisms related to the injury itself. However, how to separate those that develop allodynia from those that do not is unclear. The aims of the current study were to identify where allodynia and spasticity develop and use this information to identify metrics that separate animals that develop allodynia from those that do not in order study difference in their behavior. To accomplish these aims, a standardized grid was used to localize pain on the dorsal trunk and map it to thoracic dermatomes, providing for the development of a pain score that relied on supraspinal responses and separated subgroups of animals. Similar to human studies, the development of allodynia often occurred with the development of spasticity or hyperreflexia. Moreover, the time course and prevalence of pain phenotypes (at-, above-, or below level) produced by this model were similar to that observed in humans who have sustained an SCI. However, the amount of spared spinal matter in the injured cord did not explain the development of allodynia, as was previously reported. This approach can be used to study the mechanism underlying the development of allodynia separately from mechanisms related to the injury alone.