Functional imaging of the rat cervical spinal cord

Purpose: To examine functional magnetic resonance imaging (fMRI) of the rat cervical spinal cord using painful stimulation. Materials and Methods: fMRI of the rat cervical spinal cord was performed at 9.4 T. Stimuli included injection of 25muL of capsaicin (128 mug/mL in 7.5% dimethylsulfoxide (DMSO)) into the right dorsal forepaw and electrical stimulation (15 V, 0.3 msec, 3 Hz) of the left dorsal forepaw. Results: Activation in the dorsal horn of the spinal cord, which is known to be associated with the transmission of pain, was found in all rats (N = 4) following injection of capsaicin into the dorsal forepaw. It was possible to reproduce the pain response in a given animal several times throughout the course of an experiment, provided that sufficient time was allowed between capsaicin injections. Regions of the spinal cord associated with motor and pain response were observed in functional imaging experiments involving subcutaneous electrical stimulation of the dorsal forepaw. Conclusion: Spinal fMRI using electrical stimulation an capsaicin-induced painful stimulation can be a useful tool in an animal model of pain and injury.