Segmental and descending influences on intraspinal thresholds of single C-fibers

Ian Hentall, H. L. Fields

Research output: Contribution to journalArticle

49 Citations (Scopus)

Abstract

The effect was studied of various conditioning stimuli on the threshold of single C-fibers near their spinal terminals. Spikes were recorded in L6 and L7 dorsal root ganglia of cats. A stimulating electrode in the superficial dorsal horn delivered periodic pulses whose widths were adjusted automatically to near threshold for antidromic spike production. Most units were classified according to their adequate cutaneous stimuli, as C-mechanoreceptors, high-threshold mechanoreceptors, or polymodal nociceptors. Orthodromic activity in all units increased their threshold for up to several minutes; the maximum and rate of decay depended on the amount of activity. This phenomenon parallels the hyperpolarizing afterpotential of C-fibers in peripheral nerve and, we suggest, is probably due to the aftereffect of impulses. Cutaneous conditioning stimuli were applied for 10-20s near the receptive fields of tested units, but without activating them. During the brushing of skin hair, all threshold changes were decreases; during pinching most changes were increases; during noxious heating the numbers of increases and decreases were similar. It will be necessary to analyze the responses of postsynaptic cells in order to know the physiological significance of these threshold changes. Stimulation in the nucleus raphe magnus caused in half the units higher intraspinal thresholds. If this result is causally related to the previously reported inhibition of neuronal responses in the dorsal horn by the nucleus raphe magnus (NRM), then increased thresholds could reflect either direct presynaptic inhibition or facilitation of inhibitory connections. No correlation between receptive-field classification and the response of terminals to natural cutaneous stimulation or stimulation of the NRM could be discovered. However, the terminals of all kinds of C-fibers differ from A-fibers in their reaction to noxious cutaneous and NRM stimulation, suggesting they are subject to a different system of control.

Original languageEnglish
Pages (from-to)1527-1537
Number of pages11
JournalJournal of Neurophysiology
Volume42
Issue number6
StatePublished - Dec 1 1979
Externally publishedYes

Fingerprint

Unmyelinated Nerve Fibers
Skin
Mechanoreceptors
Myelinated Nerve Fibers
Nociceptors
Spinal Ganglia
Peripheral Nerves
Hair
Heating
Electrodes
Cats
Nucleus Raphe Magnus

ASJC Scopus subject areas

  • Physiology
  • Neuroscience(all)

Cite this

Segmental and descending influences on intraspinal thresholds of single C-fibers. / Hentall, Ian; Fields, H. L.

In: Journal of Neurophysiology, Vol. 42, No. 6, 01.12.1979, p. 1527-1537.

Research output: Contribution to journalArticle

Hentall, Ian ; Fields, H. L. / Segmental and descending influences on intraspinal thresholds of single C-fibers. In: Journal of Neurophysiology. 1979 ; Vol. 42, No. 6. pp. 1527-1537.
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