Low Doses of Fentanyl Block Central Sensitization in the Rat Spinal Cord In Vivo

Background: -Opioid receptor agonists are strong analge-sics. However, their usefulness for preemptive analgesia is con-troversial. The authors tested antinociceptive and preemptive properties of fentanyl as a -opioid receptor agonist in a model of spinal nociception in vivo. Methods: C fiber–evoked potentials were recorded in the superficial laminae I–II of the rat lumbar spinal cord with glass microelectrodes in response to electrical stimulation of the sciatic nerve. High-frequency stimulation was applied on the sciatic nerve to induce long-term potentiation of C fiber–evoked field potentials, a form of central sensitization. To test the effect of fentanyl on acute nociception, fentanyl was infused intrave-nously at increasing doses (6–192 g · kg1 · h1). One hour after start of infusion, high-frequency stimulation was applied to evaluate effects of fentanyl on the induction of long-ter