Vernon W-H Lin1, Ian Hsiao, Wade S Kingery. 1. Functional Magnetic Stimulation Laboratory, Spinal Cord Injury/Disorder, Health Care Group, VA Long Beach Health Care System, CA 90822, USA. vernon.lin@med.va.gov
Abstract
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 rat's 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 alpha(2) 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.
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 rat's 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 alpha(2) 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.