Spinal Cord and Brain Pain FMRI in Rats: Anatomical Sites of Analgesic Action of Buprenorphine on the Noxious Electrical Stimulation-Induced Pain

Fuqiang Zhao¹, Denise Welsh¹, Mangay Williams¹, Alexandre Coimbra¹, Mark O. Urban², Richard Hargreaves², Jeffrey Evelhoch¹, Donald S. Williams¹

To validate the fMRI signals in the spinal cord and the brain of rats induced by noxious stimulation as a pain biomarker, and to determine its utility in elucidation of mechanisms of action of analgesics, the effect of buprenorphine (BPN), a partial -opioid agonist, on pain fMRI signals was investigated. The pain fMRI signals in the caudate putamen and thalamus region were totally suppressed, while those in spinal cord, cerebellum, thalamic relay of somatosensory pathway, and primary somatosensory cortex were only partially (if at all) suppressed. Such a suppression pattern is consistent with the density of opioid receptor distribution in brain, supporting the idea that fMRI can provide anatomical action sites of the analgesics, which should help to understand their mechanisms of action.