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.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Category of submission: Original Article
Funding Source Statement: This work was supported by the National Institute of Health NINDS R01NS096971.
Conflicts of Interest: The authors declare no conflicts of interest.
Significance Statement: A pain score was developed that separates animals that develop at-level allodynia from those that do not in rat model of mid-thoracic contusion. Allodynia was localized to thoracic dermatomes T4-T11 and could be identified by only considering audible vocalization and avoidance behaviors. Similar to humans, trunk allodynia often occurred without allodynia at other levels, was distinguishable from the development of spasticity and hyperreflexia and developed early after SCI, suggesting this model could be used to study mechanisms underlying chronic pain.