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Acta Physiologica 2009; Volume 195, Supplement 669
The 88th Annual Meeting of The German Physiological Society
3/22/2009-3/25/2009
Giessen, Germany
EFFECTS OF LOCAL LIDOCAINE APPLICATION ON CONDUCTIVE PROPERTIES OF HUMAN C-FIBERS
Abstract number: P364
Namer1 B., Kleggetveit2 I.-P., Schmidt3 R., Jorum2 E., Handwerker1 H. O., Schmelz4 M.
1Dept. for Physiology and Pathophysiology, University of Erlangen, Erlangen
2Clinical Neurophysiology, Rikshospitalet, Oslo, Norway
3Clinical Neurophysiology, Akademiska Hospitalet, Uppsala, Sweden
4Anesthesiology, University of Mannheim, Mannheim
Mutations of axonal sodium channels such as (NAV 1.7) are linked to chronic painful conditions, but also to insensitivity to pain. Thus, modulation of axonal excitability is of crucial interest for neuropathic pain. Microneurography was used to record from unmyelinated nerve fibers (C-units) in cutaneous fascicles of the peroneal nerve in awake healthy human subjects. Sympathetic fibers were detected by a response to startle stimulation and by their characteristic pattern of activity dependant conduction velocity slowing (slowing) to 2 Hz stimulation. Afferent fibers were classified according to mechanical responsiveness. Conduction parameters (conduction velocity (CV) and slowing to different frequencies of electrical stimulation ranging from 0.125 to 2 Hz) were tested before and after local lidocaine injection. Lidocaine 0.1% 100ul was injected intradermally into the innvervation territory beneath the electrical stimulation site of the fiber endings and therby treating about 1 cm of the terminal branches of the fibers.
CV was reduced after lidocaine injection (CM from 1.3 to 0.9 m/s and symp from 1.1 to 0.7 m/s). In CM fibers activity dependent slowing upon increasing stimulation frequencies (0.125, 0.25, 0.5 Hz) changed to activity dependent speeding after lidocaine injection. The speeding never led to higher CV as in the unconditioned state before lidocaine injection. In sympathetic fibers slowing was slightly reduced after lidocaine, but no speeding was observed. During stimulation with 2 Hz for 3 min an initial speeding was observed in 50% of all CM fibers (n=10) followed by slowing. In sympathetic fibers (n=6) no speeding was observed and the characteristic slowing pattern to 3 min 2 Hz stimulation was not changed.
Conclusion:
Modulation of axonal excitability changes can be tested pharmacologically in human. The different effects of lidocaine on afferent and efferent fibers suggest differential patterns of sodium channel expression and potentially resting membrane potential in different C-fiber classes.
Supported by AstraZeneca R&D
To cite this abstract, please use the following information:
Acta Physiologica 2009; Volume 195, Supplement 669 :P364