Why are sensory axons more vulnerable for ischemia than motor axons?

• Published in: PloS one Vol. 8; no. 6; p. e67113
• Main Authors: Hofmeijer, Jeannette, Franssen, Hessel, van Schelven, Leonard J, van Putten, Michel J A M
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 20.06.2013; Public Library of Science (PLoS)
• Subjects: Action Potentials; Adult; Arm - blood supply; Arm - physiopathology; Axons; Axons - physiology; Biology; Cell Hypoxia; Conductance; Deactivation; Depolarization; Diabetes; Diabetic neuropathy; Electrodes; Excitability; Experiments; Female; Forearm; Humans; Inactivation; Ion channels; Ischemia; Ischemia - physiopathology; Male; Measurement methods; Median nerve; Medicine; Middle Aged; Motor neurons; Motor Neurons - physiology; Muscles; Nerve conduction; Neural Conduction; Neurology; Neurosciences; Proprioception; Refractory period; Resistance; Sensory neurons; Sensory Receptor Cells - physiology; Sodium conductance; Studies; Time constant; Netherlands
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0067113

In common peripheral neuropathies, sensory symptoms usually prevail over motor symptoms. This predominance of sensory symptoms may result from higher sensitivity of sensory axons to ischemia. We measured median nerve compound sensory action potentials (CSAPs), compound muscle action potentials (CMAPs), and excitability indices in five healthy subjects during forearm ischemia lasting up to disappearance of both CSAPs and CMAPs. ISCHEMIA INDUCED: (1) earlier disappearance of CSAPs than CMAPs (mean ± standard deviation 30±5 vs. 46±6 minutes), (2) initial changes compatible with axonal depolarization on excitability testing (decrease in threshold, increase in strength duration time constant (SDTC) and refractory period, and decrease in absolute superexcitability) which were all more prominent in sensory than in motor axons, and (3) a subsequent decrease of SDTC reflecting a decrease in persistent Na(+) conductance during continuing depolarisation. Our study shows that peripheral sensory axons are more vulnerable for ischemia than motor axons, with faster inexcitability during ischemia. Excitability studies during ischemia showed that this was associated with faster depolarization and faster persistent Na(+) channel inactivation in sensory than in motor axons. These findings might be attributed to differences in ion channel composition between sensory and motor axons and may contribute to the predominance of sensory over motor symptoms in common peripheral neuropathies.