Partial reversal of conduction slowing during repetitive stimulation of single sympathetic efferents in human skin
Article first published online: 19 OCT 2004
Acta Physiologica Scandinavica
Volume 182, Issue 3, pages 305–311, November 2004
How to Cite
Campero, M., Serra, J., Bostock, H. and Ochoa, J. L. (2004), Partial reversal of conduction slowing during repetitive stimulation of single sympathetic efferents in human skin. Acta Physiologica Scandinavica, 182: 305–311. doi: 10.1111/j.1365-201X.2004.01357.x
- Issue published online: 19 OCT 2004
- Article first published online: 19 OCT 2004
- Received 25 August 2003, accepted 12 July 2004
- conduction velocity;
- nerve fibres;
Aims: To describe and identify the function of a class of human C fibre with an unusual response to repetitive electrical stimulation. Other C fibres slow progressively at 2 Hz (type 1), reach a latency plateau (type 2) or hardly slow at all (type 3).
Methods: C fibres innervating hairy skin were recorded by microneurography in the superficial peroneal nerves of 19 healthy volunteers. Baseline electrical stimulation of the skin was at 0.25 Hz, and activity-dependent slowing recorded during stimulation at 2 Hz for 3 min and after a 3-min pause in stimulation.
Results: In 41 units, there was a partial recovery of latency during repetitive stimulation. These were classified as ‘type-4’ units, and identified as sympathetic efferents, since they exhibited spontaneously activity, which was enhanced by manoeuvres that increase sympathetic outflow (15 of 16 cases) and/or suppressed by a proximal anaesthetic block (eight of eight cases). The peak slowing during 2 Hz trains averaged 6.47 ± 2.06% (mean ± SD, n = 41), but after 3 min the slowing had reduced to 4.90 ± 2.20%, which was less than in all type 1 (nociceptor) fibres but similar to that in type 2 (cold) fibres. Compared with cold fibres, type-4 sympathetic fibres slowed more after the first 10 impulses at 2 Hz (2.57 ± 0.45%) and also after a pause in stimulation (1.66 ± 0.51%).
Conclusions: The distinctive activity-dependent slowing profiles of these type-4 sympathetic C units may help identification in vitro, and suggest that hyperpolarization-activated channels have a particularly prominent role in the axonal membrane.