Innervation territories of single sympathetic C-fibers in human skin.
M. Schmelz . R. Schmidt1 A. Bickel H. E. Torebjrk and H. Handwerker.
Department of Clinical Neurophysiology, University Hospital, S-75185
Uppsala, Sweden Department of Physiology I, University of Erlangen/Nrnberg,
D-91054 Erlangen, Germany.
APStracts 4:374N, 1997.
ABSTRACT
Microneurography techniques were used to record action potentials from
unmyelinated nerve fibers (C-fibers) in the cutaneous fascicles of the
peroneal nerve in healthy volunteers. C-units were identified by their long
latency responses to electrical stimulation of their terminals in the skin.
Their responsiveness to mechanical or heat stimuli applied to the skin or to
sympathetic reflex provocation tests was determined by transient slowing of
conduction velocity following activation (marking technique). In a sample of
381 C-units, 59 were unresponsive to mechanical and thermal stimulation of
their endings, but responded to sympathetic reflex provocation tests, e.g.
arousal or deep inspiration. They were classified as sympathetic efferent
units. On average, conduction velocities of sympathetic units were lower (0.78
0.12 m/s) than those of mechano-heat (CMH) or mechanoresponsive (CM)
afferent C-units (0.910.14m/s). Endings of most of the
sympathetic units were located in the skin of toes or in the foot dorsum.
Innervation territories of 16 sympathetic units were mapped by means of
conditioning transcutaneous electrical stimuli. Twelve units had one
continuous skin territory, whereas two units had two and two other units had
three and five separate territories, respectively. The mean innervated area
was 128 mm2 (range: 24-350 mm2). Innervation territories of sympathetic units
were of approximately the same size in different skin regions on the lower
leg, foot or toes. Based on responses to whole body cooling and warming, two
units were tentatively classified as vasoconstrictor and sudomotor units,
respectively. Eleven units were tested for responsiveness to iontophoresis of
acetylcholine in their innervation territories. In five of them activity was
induced which was not due to central reflex activity but instead due to
antidromic activation from the peripheral terminals. Iontophoresis of saline
or histamine was ineffective. These findings confirm the existence of
excitatory cholinergic receptors in the terminal membrane of some sympathetic
units, possibly sudomotors.
Received 20 February 1997; accepted in final form 17 December 1997.
APS Manuscript Number J151-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 7 January 1998