Membrane properties in small cutaneous nerve fibers in humans

Introduction: Assessment of membrane properties is important for understanding the mechanisms of painful peripheral neuropathy, developing new diagnostic techniques, and screening/profiling of analgesics that target ion channels. Methods: Small cutaneous nerves were activated electrically by small diameter (0.2 mm) cathodes, and large nerves were activated by ordinary patch electrodes. This new perception threshold tracking method combines perception threshold assessment and stimulation paradigms from conventional threshold tracking. Results: The strength-duration time-constant of large fibers (580 µs ± 160 µs) was lower than the time constant of small fibers (1060 µs ± 690 µs; P < 0.01, paired t-test). Threshold electrotonus showed similar threshold reductions to sub-threshold prepulses, except for 80 ms hyperpolarizing prepulses, to which small fibers showed less threshold reduction than large fibers (repeated-measures analysis of variance, Bonferroni, P = 0.006). Conclusions: This is a reliable method to investigate the membrane properties of small cutaneous nerve fibers in humans and may be used in clinical settings as a diagnostic or profiling tool. Muscle Nerve 55: 195–201, 2017