Response of cutaneous A- and C-fiber nociceptors in the monkey to controlled-force stimuli.
The goal of this study was to determine the capacity of primary afferent nociceptive fibers (nociceptors) to encode information about noxious mechanical stimuli in primates. Teased-fiber techniques were used to record from 14 A-fiber nociceptors and 18 C-fiber nociceptors that innervated the hairy skin. Stimulus-response functions were examined with an ascending series of force-controlled stimuli. Stimulus-interaction effects were examined with use of a series of paired stimuli in which the interval between the stimulus pairs was varied systematically. Both A-fiber and C-fiber nociceptors exhibited a slowly adapting response to the stepped force stimuli. The response of the A fibers increased monotonically with increasing force, whereas the response of the C fibers reached a plateau at low force levels. The slope of the stimulus-response function for the A fibers was significantly steeper than that for the C fibers, and the total response was greater. The A fibers also provided more discriminative information regarding stimulus intensity. The C fibers demonstrated a significant fatigue in response when the interstimulus interval between the paired stimuli was </=150 s, whereas the A fibers did not demonstrate a significant fatigue until the interstimulus interval was </=30 s. This fatigue in response was not due to changes in tissue compliance. These results suggest that A- and C-fiber nociceptors have different mechanical transduction mechanisms. A-fiber nociceptors exhibit steeper stimulus-response functions and less fatigue than C-fiber nociceptors.
Slugg
R M
RM
Department of Neurosurgery, Johns Hopkins University, Baltimore, Maryland 21287, USA.
Meyer
R A
RA
Campbell
J N
JN
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D003187:Compliance; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005552:Forelimb; D000882:Haplorhini; D006358:Hot Temperature; D009412:Nerve Fibers / Q000145:classification / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology* / Q000648:ultrastructure; D009619:Nociceptors / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010812:Physical Stimulation; D012867:Skin / Q000294:innervation; D013314:Stress, Mechanical