PT  - JOURNAL ARTICLE
AU  - C. Weidner
AU  - M. Schmelz
AU  - R. Schmidt
AU  - B. Hansson
AU  - H. O. Handwerker
AU  - H. E. Torebjörk
TI  - Functional Attributes Discriminating Mechano-Insensitive and Mechano-Responsive C Nociceptors in Human Skin
AID  - 10.1523/JNEUROSCI.19-22-10184.1999
DP  - 1999 Nov 15
TA  - The Journal of Neuroscience
PG  - 10184--10190
VI  - 19
IP  - 22
4099  - http://www.jneurosci.org/content/19/22/10184.short
4100  - http://www.jneurosci.org/content/19/22/10184.full
SO  - J. Neurosci.1999 Nov 15; 19
AB  - Microneurography was used in healthy human subjects to record action potentials from unmyelinated nerve fibers (C units) in cutaneous fascicles of the peroneal nerve.Activity-dependent slowing (n = 96) and transcutaneous electrical thresholds (n = 67) were determined. Eight units were sympathetic efferents according to their responses to sympathetic reflex provocations. Mechano-heat-responsive C units (CMH) (n = 56) had thresholds to von Frey hair stimulation ≤90 mN (6.5 bar). Mechano-insensitive C units (n = 32) were unresponsive to 750 mN (18 bar). Twenty-six mechano-insensitive units responded to heat (CH), and the remaining six units did not respond to physical stimuli but were proven to be afferent by their response to intracutaneous capsaicin (CMiHi).Mechano-insensitive units had significantly slower conduction velocity (0.81 ± 0.03 m/sec), and CH units had higher heat thresholds (48.0 ± 0.6°C) compared with CMH units (1.01 ± 0.01 m/sec; 40.7 ± 0.4°C). Transcutaneous electrical thresholds were <9 mA for CMH units and >35 mA for CH and CMiHi units. Activity-dependent slowing was much more pronounced in mechano-insensitive than in mechano-responsive units, without overlap. Sympathetic efferent C units showed intermediate slowing, significantly different from CMH, and completely separate from CH and CMiHi units. The activity-dependent slowing of conduction provides evidence for different membrane attributes of different classes of C fibers in humans.