Quantifying blood-spinal cord barrier permeability after peripheral nerve injury in the living mouse

Background: Genetic polymorphisms, gender and age all influence the risk of developing chronic neuropathic pain following peripheral nerve injury (PNI). It is known that there are significant inter-strain differences in pain hypersensitivity in strains of mice after PNI. In response to PNI, one of the earliest events is thought to be the disruption of the blood-spinal cord barrier (BSCB). The study of BSCB integrity after PNI may lead to a better understanding of the mechanisms that contribute to chronic pain. Results: Here we used in vivo dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to establish a timecourse for BSCB permeability following PNI, produced by performing a spared nerve injury (SNI). From this longitudinal study, we found that the SNI group had a significant increase in BSCB permeability over time throughout the entire spinal cord. The BSCB opening had a delayed onset and the increase in permeability was transient, returning to control levels just over one day after the surgery. We also examined inter-strain differences in BSCB permeability using five mouse strains (B10, C57BL/6J, CD-1, A/J and BALB/c) that spanned the range of pain hypersensitivity. We found a significant increase in BSCB permeability in the SNI group that was dependent on strain but that did not correlate with the reported strain differences in PNI-induced tactile hypersensitivity. These results were consistent with a previous experiment using Evans Blue dye to independently assess the status of the BSCB permeability. Conclusions: DCE-MRI provides a sensitive and non-invasive method to follow BSCB permeability in the same group of mice over time. Examining differences between mouse strains, we demonstrated that there is an important genetically-based control of the PNI-induced increase in BSCB permeability and that the critical genetic determinants of BSCB opening after PNI are distinct from those that determine genetic variability in PNI-induced pain hypersensitivity.