The classification and properties of nociceptive afferent units from the skin of the anaesthetized pig.
The afferent properties of nerve fibres innervating the hairy skin of the pig hind limb were investigated by recording from 142 single units from the saphenous nerve. Identified single units were isolated using maximal electrical stimulation of the nerve trunk. Afferent units were classified on the basis of their responses to a range of stimuli, both thermal (heating to 60 degrees C and cooling to 10 degrees C) and mechanical (air jet, von Frey type filaments with forces of 0.1-250 mN, and strong pressure with a blunt needle). A-fibre units (conduction velocity 6.3-64 m/s, n = 60) fell into categories that have been described in hairy skin in other mammalian species. Most were mechanoreceptors, although seven typical A-fibre mechanical nociceptors with large, multipoint fields were also isolated. No cutaneous receptive field could be found for 15% of A-fibre units. Out of 62 C-fibre units (conduction velocity 0.49-2 m/s) 40% had no cutaneous field for pressure, heat or cold. Of the C-fibre units with cutaneous fields, 42% were polymodal nociceptors, 38% were mechanoreceptors with a variety of properties, including some excited by noxious heat, and 19% were heat-only nociceptors. C-polymodal nociceptors had large receptive fields up to 12.5 mm across and did not sensitize following strong heating. Twenty units conducted at 2-6.3 m/s, between the main C- and A-fibre bands, and were varied in their responses. Some had properties identical to C-fibre mechanoreceptors whilst four were sensitive cold thermoreceptors and one was a polymodal nociceptor. Two units were mechanical nociceptors with small receptive fields.(ABSTRACT TRUNCATED AT 250 WORDS)
Lynn
B
B
Max-Planck-Institut für physiologische und klinische Forschung, W.G. Kerckhoff-Institut, Bad Nauheim, Germany.
Faulstroh
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K
Pierau
F K
FK
D000818:Animals; D006358:Hot Temperature; D008465:Mechanoreceptors / Q000502:physiology; D009412:Nerve Fibers / Q000145:classification / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000145:classification / Q000502:physiology; D009431:Neural Conduction; D009475:Neurons, Afferent / Q000145:classification* / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000502:physiology; D012867:Skin / Q000294:innervation*; D013552:Swine