Selective Opiate Modulation of Nociceptive Processing in the Human Brain

Departments of 1 Neurology, 2 Physiology, 3 Psychiatry, 4 Internal Medicine, and 5 Biostatistics, University of Michigan, Ann Arbor, Michigan 48109; 6 Center for Sensory-Motor Interaction, Aalborg University, 9220 Aalborg, Denmark; and 7 Neurology Research Laboratories, Veterans Affairs Medical Center, Ann Arbor, Michigan 48105 Casey, Kenneth L., Peter Svensson, Thomas J. Morrow, Jonathan Raz, Cyrenius Jone, and Satoshi Minoshima. Selective Opiate Modulation of Nociceptive Processing in the Human Brain. J. Neurophysiol. 84: 525-533, 2000. Fentanyl, a µ-opioid receptor agonist, produces analgesia while leaving vibrotactile sensation intact. We used positron emission tomography (PET) to study the mechanisms mediating this specific effect in healthy, right-handed human males (ages 18-28 yr). Subjects received either painful cold ( n = 11) or painless vibratory ( n = 9) stimulation before and after the intravenous injection of fentanyl (1.5 µg/kg) or placebo (saline). Compared with cool water (29°C), immersion of the hand in ice water (1°C) is painful and produces highly significant increases in regional cerebral blood flow (rCBF) within the contralateral second somatosensory (S2) and insular cortex, bilaterally in the thalamus and cerebellum, and medially in the cerebellar vermis. Responses just below the statistical threshold (3.5