High intensity magnetic stimulation over the lumbosacral spine evokes antinociception in rats

Objectives: High intensity magnetic stimulation (MS) applied over the skin can painlessly depolarize superficial and deep nerves and we aimed to evaluate the effectiveness of MS of spinal nerves in evoking a potent analgesic response. Methods: The MS was administered to adult male Sprague–Dawley rats using a Cadwell MES-10 high-speed magnetic stimulator. A Peltier device and von Frey fibers were used to determine heat and mechanical nociceptive responses of the rats. Results: A brief (5 min) course of MS over the ratʹs lumbosacral spine produced a long-lasting (30–40 min) and robust (80–90% maximum possible effect) hindpaw antinociceptive effect to both mechanical and heat stimuli. Spinal cord transected rats had intact hindpaw nociceptive withdrawal responses, but transection eliminated MS evoked antinociception, indicating a critical extrasegmental component in the mechanism of MS antinociceptive action. The opiate receptor antagonist naloxone (5 mg/kg, i.p.) completely blocked MS evoked antinociception, demonstrating an opioidergic mechanism for MS antinociception. The α2 adrenoceptor antagonist atipamezole (5 mg/kg, i.p.) slightly reduced the MS antinociceptive response to heat and had no effect on MS antinociception for mechanical stimuli. Conclusions: These data indicate that MS can evoke a robust, long-lasting antinociceptive effect, which requires an intact supraspinal pathway and is opioidergic mediated.