title: Functional MRI of the brain detects neuropathic pain in experimental spinal cord injury.
abstract: Functional magnetic resonance imaging (fMRI) has been used to map cerebral activations related to nociceptive stimuli in rodents. Here, we used fMRI to investigate abnormally increased responses to noxious or innocuous stimuli, in a well-established rat model of chronic neuropathic pain induced by photochemical lumbar spinal cord injury. In this model, a subpopulation of rats exhibits allodynia-like hypersensitivity to mechanical and cold stimulation of the trunk area. In those rats that do not develop overt hypersensitivity after identical spinal cord injury (i.e. non-hypersensitive rats), touch evoked pain can be triggered by the opioid receptor antagonist, naloxone. We show that cerebral activations in contralateral primary somatosensory cortex (SI) are markedly correlated with different behavioural characteristics of these animals. Identical electrical stimulation, applied on trunks of spinally injured hypersensitive and non-hypersensitive rats, evoked significantly higher responses in SI of the former than the latter. Although levels of fMRI signals in SI of the trunk territory were not significantly different between normal and spinally injured non-hypersensitive rats, the administration of naloxone significantly increased fMRI signals in the non-hypersensitive rats, but not in the normal rats. We conclude that increased activation of contralateral SI is a key feature of behavioural neuropathic pain in spinally injured rats and that fMRI is an effective method to monitor experimental neuropathic pain in small animals.
authors.affiliation: Department of Neuroscience, Karolinska Institutet, Retzius vag 8, B2:4, Stockholm 171 77, Sweden Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Retzius vag 8, B2:4, Stockholm 171 77, Sweden Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet, Retzius vag 8, B2:4, Stockholm 171 77, Sweden Department of Neurosurgery, School of Medicine, Tohoku University, Sendai 980-8574, Japan.
authors.forename: Toshiki
authors.initials: T
authors.lastname: Endo
authors.forename: Christian
authors.initials: C
authors.lastname: Spenger
authors.forename: Jingxia
authors.initials: J
authors.lastname: Hao
authors.forename: Teiji
authors.initials: T
authors.lastname: Tominaga
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Wiesenfeld-Hallin
authors.forename: Lars
authors.initials: L
authors.lastname: Olson
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Xu
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D001931:Brain Mapping / Q000379:methods; D005260:Female; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009437:Neuralgia / Q000175:diagnosis* / Q000378:metabolism* / Q000473:pathology; D010147:Pain Measurement / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D013119:Spinal Cord Injuries / Q000378:metabolism* / Q000473:pathology