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Perfusion imaging of spinal cord contusion: injury-induced blockade and partial reversal by β2-agonist treatment in rats.

OBJECT
Traumatic injury to the spinal cord results in considerable delayed tissue loss. The authors investigated the extent to which ischemia occurs following contusion-induced spinal cord injury and whether ischemia exacerbates tissue damage that leads to the loss of locomotor function. They also determined if ischemia is reversed with β2-adrenoceptor agonist treatment, which has been established to be neuroprotective following contusion injury.


METHODS
The extent and role of circulation loss in spinal cord injury was determined in an established experimental model of contusion injury. The spinal cord dura mater of Wistar rats was exposed by performing a laminectomy at T-8 to T-11. Laser Doppler perfusion imaging was then used to measure microcirculation in the exposed spinal cord. After imaging, a moderately severe contusion injury was produced using a weight-drop device unto the exposed dura at T-10. Perfusion imaging was again performed, scans were quantitated, and integrated intensities were compared.


RESULTS
Postinjury imaging revealed an 18%-27% reduction in perfusion in regions rostral and caudal to the injury site, and a 68% reduction was observed at the contusion epicenter. These perfusion losses persisted for at least 48 hours. At 24 hours after injury, some rats were intraperitoneally injected with 2 mg/kg of the β2-adrenoceptor agonist clenbuterol, which has been shown to promote the partial recovery of locomotor function and spare spinal cord tissue when administered within 2 days after contusion injury. Clenbuterol injection caused a gradual increase in perfusion, which was detectable at 30 minutes postinjection and continued over time, resulting in an 127% overall increase in perfusion at the epicenter 24 hours after treatment.


CONCLUSIONS
These results suggest that the occurrence of chronic perfusion loss after contusion contributes to delayed damage and tissue loss. In contrast, β2-adrenoceptor agonist treatment may exert neuroprotection by restoring perfusion, thereby preventing ischemic neurodegeneration. The ability of laser Doppler imaging to measure the loss of perfusion and its restoration upon treatment suggests that it may have clinical utility in the assessment and treatment of spinal cord injury.