This paper has investigated the hypothesis that spinal root avulsion (SRA) injury produces alterations in blood flow that contribute to avulsion injury induced pain-like behaviour in rodents. Photoplethysmography (PPG) is an established way of assessing blood flow in the central nervous system (CNS) and laser Doppler flowmetry (LDF) is the most widely used technique for measuring tissue perfusion. Using an established model of SRA injury that produces mechanical hypersensitivity, the PPG and LDF signals were recorded in animals 2 weeks post-injury and compared to naive recordings. PPG and LDF measurements were assessed on the ipsilateral and contralateral sides of the spinal cord rostral and caudal to the avulsion injury and at the level of the injury. Two weeks after injury, a time when vascular blood vessel endothelial markers are known to be decreased, no significant changes were seen in the spinal cord blood flow (SCBF) above, at, or below the injury site or when comparing the ipsilateral vs. contralateral side. Assessment of oxygenation levels again revealed no significant differences between naive and spinal root injured animals along the rostrocaudal axis (i.e., above, at, and below the site of injury or its equivalent on the contralateral side). From these experiments it is concluded that SRA does not significantly alter blood flow or tissue oxygen levels and so ischemia may play a less prominent role in avulsion injury induced pain.
Keywords: Avulsion; doppler flowmetry; ischemia; pain; photoplethysmography; spinal cord.